United States 

Environmental 

Protection Agency 

Office of Research and Development 

Office of Water 

Washington, DC 20460 

EPA 841-B-06-002 

December 2006

www.epa.gov/owow/streamsurvey

Wadeable Streams Assessment

A Collaborative Survey of the Nation’s Streams

Eastern Highlands

Plains and Lowlands

West

WSA Major Regions*

*based on Omernik Level III ecoregions

0 10 20 30 40 50

West

Eastern

Highlands

Plains and

Lowlands

National

(lower 48)

60

Percentage of Stream Miles

Stream Length (mi)

78,346

42,527

31,247

305

Total: 152,425

87,297

49,410

117,285

26,371

Total: 276,362

125,785

49,454

65,715

1,310

Total: 242,264

290,565

138,908

213,394

28,184

Total: 671,051

43.3%

20.7%

31.8%

4.2%

L

M

H

N/A

31.6%

16.4%

42.4%

9.5%

L

M

H

N/A

20.4%

27.1%

0.5%

L 51.9%

M

H

N/A

27.9%

20.5%

L 51.4%

M

H

N/A 0.2%

Good Fair Poor Not Assessed

A Collaborative Survey of the Nationʼs Streams
Front cover photo courtesy of the Colorado Division of Wildlife 

Inside cover photo courtesy of Michael L. Smith, U.S. Fish and Wildlife Service 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

i

Acknowledgments

This report resulted from a ground-breaking collaboration on stream monitoring. States came together 

with the U.S. Environmental Protection Agency (EPA) to demonstrate a cost-effective approach for 

answering one of the nation’s most basic water quality questions: What is the condition of our nation’s 

streams?

The EPA Office of Water would like to thank the many participants who contributed to this important 

effort and the scientists within the EPA Office of Research and Development for their research and 

refinement of the survey design, field protocols, and indicator development. Through the collaborative 

efforts of state environmental and natural resource agencies, federal agencies, universities, and other 

organizations, more than 150 field biologists were trained to collect environmental samples using a 

standardized method, and more than 25 taxonomists identified as many as 500 organisms in each sample. 

Each participating organization attended a national meeting to discuss and formulate the data analysis 

approach, as well as regional meetings to evaluate and refine the results presented in this report. 

Collaborators

Alaska Department of Environmental Conservation

Arizona Game and Fish Department

Arkansas Department of Environmental Quality

California Department of Fish and Game

California State Water Resources Control Board

Colorado Department of Public Health and 

Environment

Colorado Division of Wildlife

Connecticut Department of Environmental Protection

Delaware Department of Natural Resources 

and Environmental Control 

Georgia Department of Natural Resources

Idaho Department of Environmental Quality

Illinois Environmental Protection Agency

Iowa Department of Natural Resources

Kansas Department of Health and Environment

Kentucky Division of Water

Louisiana Department of Environmental Quality

Maine Department of Environmental Protection

Maryland Department of Natural Resources

Michigan Department of Environmental Quality 

Minnesota Pollution Control Agency

Mississippi Department of Environmental Quality

Missouri Department of Conservation 

Montana Department of Environmental Quality

Nevada Division of Environmental Protection

New Hampshire Department of Environmental 

Services

New Jersey Department of Environmental Protection

New Mexico Environment Department

New York State Department of Environmental 

Conservation

North Carolina Division of Water Quality

North Dakota Department of Health

Ohio Environmental Protection Agency

Oklahoma Conservation Commission

Oklahoma Water Resources Board

Oregon Department of Environmental Quality

Pennsylvania Department of Environmental Protection

South Carolina Department of Health 

and Environmental Control

South Dakota Department of Environment 

and Natural Resources

South Dakota Game, Fish and Parks

Tennessee Department of Environment and 

Conservation

Texas Commission of Environmental Quality
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

ii

Utah Division of Water Quality

Vermont Department of Environmental Conservation

Virginia Department of Environmental Quality

Washington State Department of Ecology

West Virginia Department of Environmental 

Protection

Wisconsin Department of Natural Resources

Wyoming Department of Environmental Quality

Fort Peck Assiniboine and Sioux Tribes

Guam Environmental Protection Agency

U.S. Geological Survey

U.S. EPA, Office of Environmental Information

U.S. EPA, Office of Water

U.S. EPA, Office of Research and Development

U.S. EPA, Regions 1–10

Center for Applied Bioassessment and Biocriteria

Central Plains Center for Bioassessment

New England Interstate Water Pollution Control 

Commission

The Council of State Governments

Great Lakes Environmental Center

Tetra Tech, Inc.

EcoAnalysts

University of Arkansas

Mississippi State University 

Oregon State University

Utah State University 

The data analysis team painstakingly reviewed the data set to ensure its quality and performed the data 

analysis. This team included Phil Kaufmann, Phil Larsen, Tony Olsen, Steve Paulsen, Dave Peck, John 

Stoddard, John Van Sickle, and Lester Yuan from the EPA Office of Research and Development; Alan 

Herlihy from Oregon State University; Chuck Hawkins from Utah State University; Daren Carlisle from 

the U.S. Geological Survey; and Michael Barbour, Jeroen Gerritson, Erik Lepow, Kristen Pavlik, and Sam 

Stribling from Tetra Tech, Inc.

The report was written by Steve Paulsen and John Stoddard from the EPA Office of Research and 

Development and Susan Holdsworth, Alice Mayio, and Ellen Tarquinio from the EPA Office of Water. 

Major contributions to the report were made by John Van Sickle, Dave Peck, Phil Kaufmann, and Tony 

Olsen from the EPA Office of Research and Development and Peter Grevatt and Evan Hornig from EPA 

Office of Water, Alan Herlihy from Oregon State University, Chuck Hawkins from Utah State University, 

and Bill Arnold from the Great Lakes Environmental Center. Technical editing and document production 

support was provided by RTI International. This report was significantly improved by the external peer 

review conducted by Dr. Stanley V. Gregory, Ecologist, Oregon State University; Dr. Kenneth Reckhow, 

Environmental Engineer, Duke University; Dr. Kent Thornton, Principal Ecologist, FTN Associates; Dr. 

Scott Urquhart, Statistician, Colorado State University; and Terry M. Short of the U.S. Geological Survey. 

The Quality Assurance Officer for this project was Otto Gutenson from the EPA Office of Water.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

iii

Table of Contents

Acknowledgments .............................................................................................................................ii

 Collaborators .................................................................................................................................iii

Executive Summary ..................................................................................................................... ES-2

Introduction ......................................................................................................................................2

Chapter 1 – Design of the Wadeable Streams Assessment ..............................................................6

 Why focus on wadeable streams? .....................................................................................................6

 What area does the WSA cover? ......................................................................................................9

 What areas are used to report WSA results? ...................................................................................13

 How were sampling sites chosen? ...................................................................................................15

 How were waters assessed? .............................................................................................................19

 Setting expectations .......................................................................................................................23

Chapter 2 – Condition of the Nation’s Streams ............................................................................26

 Background ...................................................................................................................................26

 Indicators of Biological Condition .................................................................................................26

 Macroinvertebrate Index of Biotic Condition ............................................................................28

 Macroinvertebrate Observed/Expected (O/E) Ratio of Taxa Loss ...............................................31

 Aquatic Indicators of Stress ...........................................................................................................33

 Chemical Stressors ....................................................................................................................33

 Physical Habitat Stressors ..........................................................................................................39

 Biological Stressors ....................................................................................................................45

 Ranking of Stressors ......................................................................................................................46

 Extent of Stressors .....................................................................................................................46

 Relative Risk of Stressors to Biological Condition......................................................................48

 Combining Extent and Relative Risk ........................................................................................50

Chapter 3 – Wadeable Streams Assessment Ecoregion Results .....................................................52

 Northern Appalachians Ecoregion .................................................................................................54

 Physical Setting .........................................................................................................................54

 Biological Setting ......................................................................................................................54

 Human Influence ......................................................................................................................54

 Summary of WSA Findings .......................................................................................................55

 Southern Appalachians Ecoregion .................................................................................................58

 Physical Setting .........................................................................................................................58

 Biological Setting ......................................................................................................................58

 Human Influence ......................................................................................................................59

 Summary of WSA Findings .......................................................................................................59
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

iv

 Coastal Plains Ecoregion ...............................................................................................................61
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

v

Chapter 4 – Summary and Next Steps ...........................................................................................86

 Summary ......................................................................................................................................86

 Next Steps .....................................................................................................................................88

Glossary of Terms ............................................................................................................................91

Sources and References ...................................................................................................................93

 General References ........................................................................................................................93

 Stream and River Sampling and Laboratory Methods ....................................................................94

 Probability Designs .......................................................................................................................95

 Ecological Regions ........................................................................................................................95

 Indices of Biotic Integrity ..............................................................................................................96

 Observed/Expected Models ...........................................................................................................96

 Physical Habitat ............................................................................................................................96

 Reference Condition .....................................................................................................................97

 Other EMAP Assessments .............................................................................................................97

 Biological Condition Gradient/Quality of Reference Sites .............................................................97

 Relative Risk .................................................................................................................................97

 Nutrients.......................................................................................................................................98
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

vi

Figures

 1 Strahler stream order diagram .................................................................................................7

 2 Stream characteristics change as the stream’s size or stream order increases ...............................8

 3 Major rivers and streams of the conterminous United States ...................................................9

 4 Average annual precipitation of the United States, 1961–1990 ..............................................10

 5 Major land cover patterns of the conterminous United States ................................................11

 6 Human population density (people per square mile) based on the 

 2000 U.S. Census Bureau data .........................................................................................12

 7 Three major regions were surveyed for the WSA ...................................................................13

 8 Nine ecoregions were surveyed for the WSA .........................................................................14

 9 Length of wadeable, perennial streams in each WSA ecoregion .............................................16

 10 Sites sampled for the WSA by EPA Region ...........................................................................17

 11 Reach layout for sampling .....................................................................................................19

 12 Stream macroinvertebrates ....................................................................................................20

 13 Biological condition of streams based on Macroinvertebrate Index of Biotic Condition .........30

 14 Macroinvertebrate taxa loss as measured by the O/E Ratio of Taxa Loss ................................32

 15 Total phosphorus concentrations in U.S. streams ..................................................................35

 16 Total nitrogen concentrations in U.S. streams .......................................................................36

 17 Salinity conditions in U.S. streams ........................................................................................37

 18 Acidification in U.S. streams .................................................................................................39

 19 Streambed sediments in U.S. streams ....................................................................................41

 20 In-stream fish habitat in U.S. streams....................................................................................42

 21 Riparian vegetative cover in U.S. streams ..............................................................................43

 22 Riparian disturbance in U.S. streams ....................................................................................45

 23 Extent of stressors .................................................................................................................47

 24 Extent of stressors and their relative risk to Macroinvertebrate Condition 

 and O/E Taxa Loss ...........................................................................................................49

 25 Ecoregions surveyed for the WSA .........................................................................................53

 26 WSA survey results for the Northern Appalachians ecoregion ...............................................56

 27 WSA survey results for the Southern Appalachians ecoregion ................................................60

 28 WSA survey results for the Coastal Plains ecoregion ..............................................................63

 29 WSA survey results for the Upper Midwest ecoregion ...........................................................67

 30 WSA survey results for the Temperate Plains ecoregion .........................................................70

 31 WSA survey results for the Southern Plains ecoregion ...........................................................72

 32 WSA survey results for the Northern Plains ecoregion ...........................................................75

 33 WSA survey results for the Western Mountains ecoregion .....................................................79

 34 WSA survey results for the Xeric ecoregion ...........................................................................83
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

vii

Acronym List

 ̊F degrees Fahrenheit

ANC acid neutralizing capacity

BMPs best management practices

CAAA Clean Air Act Amendments

CWA Clean Water Act

EMAP Environmental Monitoring and Assessment Program

EPA U.S. Environmental Protection Agency

FWS U.S. Fish and Wildlife Service

km kilometers

mi2

 square miles

NAPAP National Acid Precipitation Program

NCA National Coastal Assessment

NCCR National Coastal Condition Report

NCCR II National Coastal Condition Report II

NEP National Estuary Program 

NEP CCR National Estuary Program Coastal Condition Report

NHD National Hydrography Dataset

NLCD National Land Cover Dataset

NOAA National Atmospheric and Oceanic Administration

O/E observed/expected

PCBs polychlorinated biphenyls

RBS relative bed stability

TDS total dissolved solids

μeq/L microequivalents per liter

USGS U.S. Geological Survey

VOCs volatile organic compounds

WSA Wadeable Streams Assessment

Executive Summary

Photo courtesy of Monty Porter
Executive Summary 

ES-4

The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

-4 ES-4

Executive Summary

“I started out thinking of America as 

highways and state lines. As I got to know it 

better, I began to think of it as rivers. America

is a great story, and there is a river on every 

page of it.”

This quote by well-known journalist Charles 

Kuralt refl ects on the central role that rivers and 

streams have played in shaping the history and 

character of our nation. Because the health and 

survival of U.S. families and communities are 

dependent on these waterbodies, their condition, 

as well as how they are protected, refl ects our 

values and choices as a society. 

The Wadeable Streams Assessment (WSA) 

provides the fi rst statistically defensible summary 

of the condition of the nation’s streams and small 

rivers. In the 35 years since the passage of the 

Clean Water Act (CWA), the U.S. Congress, 

American public, and other interested parties have 

asked the U.S. Environmental Protection Agency 

(EPA) to describe the water quality condition of 

U.S. waterbodies. These requests have included 

seemingly simple questions: Is there a water 

quality problem? How extensive is the problem? 

Does the problem occur in “hotspots” or is it 

widespread? Which environmental stressors affect 

the quality of the nation’s streams and rivers, and 

which are most likely to be detrimental? This 

WSA report presents the initial results of what 

will be a long-term partnership between EPA, 

other federal agencies, states, and tribes to answer 

these questions. 

The WSA encompasses the wadeable streams 

and rivers that account for a vast majority of the 

length of fl owing waters in the United States. To 

perform the assessment, EPA, states, and tribes 

collected chemical, physical, and biological data 

at 1,392 wadeable, perennial stream locations to 

determine the biological condition of these waters 

and the primary stressors affecting their quality. 

Research teams collected samples at sites chosen 

using a statistical design to ensure representative 

results. The results of this analysis provide a clear 

assessment of the biological quality of wadeable, 

perennial streams and rivers across the country, 

as well as within each of three major climatic and 

landform regions and nine ecological regions, or 

ecoregions. 

Little Washita River, OK, in the Southern 

Plains ecoregion (Photo courtesy of Monty Porter).
Executive Summary 

ES-5

The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

ES-5

Figure ES-1. Biological condition of wadeable streams (U.S. EPA/WSA).

Good

Fair

Poor

Not Assessed

5.0%

28.2%

41.9%

24.9%

2.0% 9.5%

18.2%

27.4% 29.0%

45.1% 40.0%

20.5%

51.8%

25.8% 29.0%

1.7%

West Plains and Lowlands Eastern Highlands

152,425 miles 242,264 miles 276,362 miles

National

Biological Condition

WSA

Major Regions*

West

Plains and Lowlands

Eastern Highlands

*based on Omernik

Level III ecoregions

• Enhance the capacity of states and tribes to 

include these design and measurement tools 

in their water quality monitoring programs 

so that assessments will be ecologically and 

statistically comparable, both regionally and 

nationally.

The results of the WSA show that 42% of the 

nation’s stream length is in poor biological 

condition compared to least-disturbed reference 

sites in the nine ecoregions, 25% is in fair 

biological condition, and 28% is in good bio logical condition (Figure ES-1). Five percent of the 

nation’s stream length was not assessed for 

biological condition during the WSA. 

The information provided in this report fi lls an 

important gap in meeting the requirements of the 

CWA. The purpose of the WSA is four-fold:

• Report on the ecological (biological, chemical, 

and physical) condition of all wadeable, perennial streams and rivers within the conterminous 

United States. (Pilot assessment projects are 

also underway in Alaska and Hawaii.)

• Describe the biological condition of these 

systems using direct measures of aquatic life. 

Assessments of stream quality have historically 

relied primarily on chemical analyses of water, 

or sometimes, on the status of game fi sh.

• Identify and rank the relative importance of 

chemical and physical stressors (disturbances) 

affecting stream and river condition.
Executive Summary 

ES-6

The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

ES-6

Of the three major regions discussed in 

this report, the West is in the best biological 

condition, with 45% of stream length in good 

biological condition. The Plains and Lowlands 

region has almost 30% of stream length in good 

biological condition and 40% in poor biological 

condition. The Eastern Highlands region presents 

the most concerns, with only 18% of stream 

length in good biological condition and 52% in 

poor biological condition. 

 The WSA also examines the key factors most 

likely responsible for diminishing biological 

quality in fl owing waters, as determined by 

aquatic macroinvertebrate communities. The 

most widespread stressors observed across the 

country and in each of the three major regions 

are nitrogen, phosphorus, riparian disturbance, 

and streambed sediments. Increases in nutrients 

(e.g., nitrogen and phosphorus) and streambed 

sediments have the highest impact on biological 

condition; the risk of having poor biological 

condition was two times greater for streams 

scoring poor for nutrients or streambed sediments 

than for streams that scored in the good range for 

the same stressors (Figure ES-2). 

Understanding the current condition of the 

nation’s wadeable streams and rivers is critical 

to supporting the development of water quality 

management plans and priorities that help 

maintain and restore the ecological condition of 

these resources. This report provides a primarybaseline assessment to track water quality status 

and trends. The results of the WSA and similar 

assessments in the future will inform the public, 

water quality managers, and elected offi cials of the 

effectiveness of efforts to protect and restore water 

quality, as well as the potential need to refocus 

these efforts. 

Readers who wish to learn more about the 

technical background of the WSA are directed 

to literature cited in the References section at 

the end of this report and to material posted on 

the EPA Web site at http://www.epa.gov/owow/

streamsurvey.

Nitrogen 31.8%

Phosphorus 30.9%

Riparian Disturbance 25.5%

Streambed Sediments 24.9%

In-stream Fish Habitat 19.5%

Riparian Vegetative Cover 19.3%

Salinity 2.9%

Acidification

0 10 20 30 40

Percentage Stream Length in Most Relative Risk

Disturbed Condition

1 2 3 4

2.2%

2.2

1.4

2.4

1.4

1.6

1.7

Relative Risk to

Extent of Stressor Biological Condition

2.1

Figure ES-2. Extent of stressors and their relative risk to the biological condition of the 

nation’s streams (U.S. EPA/WSA).


Introduction

Photo courtesy of the Georgia Department of Natural Resources
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Introduction 



Introduction

In 1972, the U.S. Congress enacted the 

landmark Clean Water Act (CWA) to protect the 

nation’s vital water resources. A critical section 

of the CWA calls for periodic accounting to 

Congress and the American public on the success 

or failure of efforts to protect and restore the 

nation’s waterbodies. In recent years, a number of 

groups reviewed the available data and concluded 

that the U.S. Environmental Protection Agency 

(EPA) and state environmental agencies have been 

unable to provide Congress and the public with 

adequate information regarding the condition of 

the nation’s waterbodies. 

In 2000, the General Accounting Office issued 

a report noting that EPA and the states could not 

make statistically valid inferences about water 

quality and lacked data to support management 

decisions. A National Research Council report in 

2001 found that a uniform, consistent approach 

to ambient monitoring and data collection 

was necessary to support core water programs. 

In 2002, the National Academy of Public 

Administration and the H. John Heinz III Center 

for Science, Economics, and the Environment 

issued similar conclusions. 

Following the 2002 release of the Heinz 

Center’s report The State of the Nation’s Ecosystems, 

the national newspaper USA Today published 

an editorial discussing the lack of environmental 

information available to the public. This editorial 

emphasized the failure of state and federal agencies 

to fund the collection of necessary environmental 

data despite very effective collection of comparable 

information on the U.S. economy, population, 

energy usage, human health issues, and crime 

rate. The editorial concluded that “without such 

information, the public doesn’t know when to 

celebrate environmental successes, tackle new 

threats, or end efforts that throw money down a 

drain” (USA Today, September 21, 2002).

Little Washita River, OK, in the Southern Plains ecoregion (Photo courtesy of Monty Porter).
Introduction 



The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

To bridge this information gap, EPA, other 

federal agencies, states, and tribes, are 

collaborating to provide the public with improved 

environmental information. This collaboration 

includes a new monitoring effort to assess the 

quality of the nation’s waterbodies, an effort that 

has produced reports on three national water 

quality assessments during the past five years for 

coastal and estuarine waters (see Highlight: 

National Report on Coastal Waters). Similar efforts 

are planned for other water resource assessments 

in the future. The Wadeable Streams Assessment 

(WSA)—the first nationally consistent, 

statistically valid study of the nation’s wadeable 

streams—marks the continuation of a 

commitment to produce statistically valid 

scientific assessments of the nation’s fresh waters. 

State water quality agencies, tribes, and other 

partners, with support from EPA, conducted the 

work for the WSA using standardized methods 

at all sites to ensure the comparability of results 

across the country. Beyond yielding scientifically 

credible information on the condition and health 

of the nation’s wadeable streams, the WSA was 

designed to provide states with funding and 

expertise that enhances their ability to monitor 

and assess the quality of their waters. 

EPA and its collaborating partners plan to 

conduct similar assessments of other types of 

waterbodies (e.g., lakes, rivers, and wetlands) in 

the future, with the goal of producing updated 

assessments for each type of waterbody every 

five years. These repeated studies will ensure that 

the public remains informed as to whether the 

collective efforts to protect and restore the nation’s 

waters are meeting with success.

Photo courtesy of Gary Kramer, U.S. Department of Agriculture Natural Resources Conservation Service.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Introduction 



Highlight

National Reports on Coastal Waters

The National Coastal Assessment (NCA) surveys the condition of the nation’s coastal resources, 

as well as state efforts to protect, manage, and restore coastal ecosystems. The results of these 

surveys are compiled periodically into the National Coastal Condition Report (NCCR) series. The 

states, EPA, and partner agencies, including the National Oceanic and Atmospheric Administration 

(NOAA), U.S. Geological Survey (USGS), and U.S. Fish and Wildlife Service (FWS), issued the National 

Coastal Condition Report II (NCCR II) in January 2005 as the second in this series of reports on 

environmental surveys of U.S. coastal waters. The NCCR II includes evaluations of 100% of the 

nation’s estuaries in the conterminous 48 states and Puerto Rico. Federal, state, and local agencies 

collected more than 50,000 samples between 1997 and 2000 for the NCCR II, using nationally 

consistent methods and a probability-based design to assess five key indices of coastal water health: 

water quality, coastal habitat loss, sediment quality, benthic community condition, and fish tissue 

contaminants levels.

The National Estuary Program Coastal Condition Report (NEP CCR) focuses specifically on the 

condition of the 28 estuaries in the National Estuary Program (NEP) using data collected from 1997 

through 2003 for EPA’s NCA. The NEP CCR also presents monitoring data collected and analyzed 

by each individual NEP and its partners for a variety of estuarine quality indicators. The 28 NEPs are 

using these data to develop and implement sets of program-specific indicators of estuarine condition.
5

Chapter 1

Design of the Wadeable 

Streams Assessment

Photo courtesy of the Georgia Department of Natural Resources
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

 6

Design of the 

Wadeable Streams 

Assessment

Why Focus on Wadeable 

Streams?

Like the network of blood vessels that supply 

life-giving oxygen and nutrients to all parts 

of the human body, streams and rivers form a 

network that carries essential water to all parts 

of the nation. The human body has far more 

small capillaries than large, major arteries and 

veins; similarly, only a few U.S. rivers span large 

portions of the country (e.g., the Mississippi, 

Missouri, or Columbia rivers). Most of the 

nation’s waterways are much smaller stream 

and river systems that form an intimate linkage 

between land and water.

The WSA addresses these smaller systems, 

which ecologists often refer to as “wadeable” 

because they are small and shallow enough to 

adequately sample without a boat. Almost every 

state, university, federal agency, and volunteer 

group involved in water quality monitoring has 

experience sampling these smaller fl owing waters; 

therefore, a wide range of expertise was available 

for the WSA’s nationwide monitoring effort. 

About 90% of perennial stream and river miles 

in the United States are small, wadeable streams. 

Stream and river ecologists commonly use the 

term Strahler stream order to refer to stream size, 

and wadeable streams generally fall into the 1stthrough 5th-order range (Figure 1). First-order 

streams are the headwaters of a river, where the 

life of a river begins; as streams join one another, 

their stream order increases. It is important to 

note that many 1st-order streams, particularly 

those located in the western United States, do 

not fl ow continuously. These intermittent or 

ephemeral streams were not included in the WSA 

because well-developed indicators to assess these 

waterbodies do not yet exist. At the other end of 

the range are larger-order rivers and streams that 

Sawmill Creek, MA, in the Northern Appalachians ecoregion

(Photo courtesy of Colin Hill, Tetra Tech, Inc.).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

7

Figure 1. Strahler stream order diagram (U.S. EPA/WSA). Stream size is 

categorized by Strahler stream order, demonstrated here for a watershed. 

The confl uence (joining) of two 1st-order streams forms a 2nd-order stream; 

the confl uence of two 2nd-order streams forms a 3rd-order stream.

are too deep for wadeable sampling methods. 

These deeper waterbodies will be included in a 

future survey of non-wadeable rivers.

Stream order (stream size) affects a stream’s 

natural characteristics, including the biological 

communities that live in the stream, such as fi sh 

and invertebrates. Very small 1st-order and 2ndorder streams are often quite clear and narrow 

and are frequently shaded by grasses, shrubs, and 

trees that grow along the stream bank (Figure 2). 

The food base of these streams is found along the 

stream bank and tends to consist of leaves and 

terrestrial insects, which dominate the streams’ 

ecology, along with algae that attach to rocks and 

wood, aquatic insects adapted to shredding leaves 

and scraping algae, and small fi sh that feed on 

these organisms. In contrast, larger 6th- and 7thorder rivers typically appear muddy because their 

fl ow carries accumulated sediments downstream. 

These rivers are wide enough that the canopy 

cover along their banks shades only a narrow 

margin of water along the river’s edge. The food 

base for these waterbodies shifts towards instream sources, such as algae; downstream drift of 

small organisms; and deposition of fi ne detritus. 

Although the aquatic communities of larger rivers 

include the algae and terrestrial insects found in 

streams, these rivers are dominated by insects 

adapted to fi ltering and gathering fi ne organic 

particles, and larger fi sh that are omnivorous 

(feeding on plants and animals) and/or 

piscivorous (feeding on smaller fi sh).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Figure 2. Stream characteristics change as the stream’s size or stream order increases

(Vannote et al., 1980). 

Chapter 1 Design of the Wadeable Streams Assessment

8
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

9

What Area Does the WSA Cover?

This WSA encompasses the wadeable streams 

of the conterminous United States, or lower 48 

states (Figure 3). This land area covers 3,007,436 

square miles (mi2

) and includes private, state, 

tribal, and federal land. Although not included 

in this report, initial stream-sampling projects 

outside the conterminous United States have 

begun and will be included in future assessments. 

For example, scientists in Alaska sampled streams 

in the Tanana River Basin (a subbasin to the 

Yukon River) during 2004 and 2005, and they 

expect to report their results in 2007; Guam has 

begun implementation of a stream survey; and 

Puerto Rico is developing indicators for assessing 

the condition of its tropical streams. In addition, 

the State of Hawaii began stream sampling using 

WSA techniques on the island of Oahu in 2006.

State boundaries offer few insights into the 

true nature of features that mold our streams and 

rivers. The most fundamental trait that defi nes 

U.S. waters is annual precipitation (Figure 4). 

A sharp change occurs on either side of the 

Figure 3. Major rivers and streams of the conterminous United States (NationalAtlas.gov, 2006). 

Major rivers comprise only 10% of the length of U.S. fl owing waters, whereas the nation’s wadeable streams 

and rivers comprise 90% of the length of U.S. fl owing waters. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

10

100th longitude that runs from west Texas 

through North Dakota, with precipitation falling 

plentifully to the east, but sparsely to the west. 

(The high mountains of the western United 

States and the Pacifi c coast are exceptions to the 

general scarcity of water in the West.) The eastwest divide in moisture has not only shaped the 

character of the nation’s waters, but also how they 

are used, valued, and the even the legal systems 

with which they are managed. A second divide 

that defi nes the nature of U.S. rivers and streams 

is the north-south gradient in temperature. 

Figure 4. Average annual precipitation of the United States, 1961–1990 (NOAA, National Climatic 

Data Center). The 100th longitude meridian runs from Texas north through North Dakota and reveals a major 

gradient of precipitation that defi nes differences in western and eastern streams. 

Annual Average Precipitation

(in inches) 1961–1990

<5

5–10

10–15

15–20 60–70

20–25 70–80

25–30 80–100

30–35 100–120

35–40 120–140

40–50 140–180

50–60 180–200

Young Womans Creek, PA, in the Southern 

Appalachians ecoregion (Photo courtesy of the 

Great Lakes Environmental Center). 
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Chapter 1 Design of the Wadeable Streams Assessment

11

The nation includes a wide diversity of 

landscapes, from the varied forests of the East, to 

the immense agricultural plains and grasslands 

of the Midwest, to the deserts and shrublands 

of the Southwest, to the giant mountain ranges 

of the West (Figure 5). In the eastern part of the 

country, the Appalachian mountains run from 

Maine to Alabama, crossing climatic boundaries 

and separating the waters fl owing to the Atlantic 

Ocean from those fl owing to the Gulf of Mexico. 

The larger mountain ranges in the West link 

their landscapes together: the Rockies through 

the heart of the West; the Cascades, which 

crown the Northwest in snow; the Sierra Nevada 

in California; and the Coastal Range, which 

plummets to the Pacifi c Ocean, with a fault-block 

shoreline that stretches from the Santa Monica 

mountains to Kodiak Island. The Coastal Plains 

of the East and Southeast and the Great Plains of 

the interior provide other major landform features 

that mark the country.

Figure 5. Major land cover patterns of the conterminous United States (USGS, 2000).

Land Cover*

Forest

Agriculture

Wetland

Shrubland

Urban

Bare

*based on NLCD 1992
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Chapter 1 Design of the Wadeable Streams Assessment

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The establishment and spread of European 

colonies and the Industrial Revolution intensifi ed 

the transformation of the nation’s natural 

landscape, as greater numbers of people arrived 

and modifi ed many of the features of the land and 

waters. As the nation’s population grew and cities 

and towns were established, tens of thousands 

of dams were constructed to alter the fl ow of 

virtually every major river in the United States. 

Historically, people have tended to live where 

water is more abundant. Current population 

patterns based on 2000 U.S. Census Bureau 

data refl ect the historical abundance of waters 

in the East and forecast the growing challenges 

facing the water-scarce regions in the West, where 

population has grown in recent years (Figure 

6). The current and future condition of the 

nation’s waters will continue to be infl uenced 

by population patterns, as well as how the 

components of a watershed, including surface 

water, groundwater, and the land itself, are used. 

Figure 6. Human population density (people per square mile) based on 2000 U.S. Census 

Bureau data (ESRI, 2005).

Population

Density 2000

(people per square mile)

<1 25–49

1–4 50–99

5–9 100–249

10–24 >250
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Chapter 1 Design of the Wadeable Streams Assessment

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What Areas Are Used to Report 

WSA Results?

The conterminous United States is the 

broadest-scale unit for which WSA results are 

reported. For this report, this area has been split 

into three major regions—the Eastern Highlands, 

the Plains and Lowlands, and the West. These 

three regions correspond to major climate and 

landform patterns across the United States 

(Figure 7). 

The Eastern Highlands region is composed 

of the mountainous areas east of the Mississippi 

River and includes the piedmont to the east 

of the Appalachians and the interior plateau 

to their west. The Plains and Lowlands region 

encompasses the Atlantic and Gulf of Mexico 

coastal plains and the lowlands of the Mississippi 

Delta, as well as the portions of the Midwest from 

the Dakotas down through most of Texas. The 

West region includes the western portion of the 

country, from the desert southwestern United 

States and the Rocky Mountains to the Pacifi c 

Ocean. Chapter 2 of this report describes the 

WSA results for these three major regions.

Figure 7. Three major regions were surveyed for the WSA (U.S. EPA/WSA).

WSA Major Regions*

Eastern Highlands

Plains and Lowlands

West

*based on Omernik Level III ecoregions
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Chapter 1 Design of the Wadeable Streams Assessment

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A fi ner-scale reporting unit included in 

the WSA consists of nine ecological regions 

(ecoregions) (Figure 8) that further divide the 

three major regions. The three major regions 

and the nine ecoregions outlined in this report 

are aggregations of smaller ecoregions defi ned by 

EPA. Areas are included in an ecoregion based 

on similar landform and climate characteristics. 

For example, water resources within a particular 

ecoregion have similar natural characteristics and 

respond similarly to natural and anthropogenic 

stressors. Typically, management practices aimed 

at preventing degradation or restoring water 

quality apply to many fl owing waters with similar 

problems throughout an ecoregion. This report 

presents results by ecoregions because the patterns 

of response to stress, and the stressors themselves, 

are often best understood in a regional context. 

The results for the nine ecoregions are reviewed in 

Chapter 3 of this report. 

The Eastern Highlands region is divided into 

two ecoregions: the Northern Appalachians 

ecoregion, which encompasses New England, 

New York, and northern Pennsylvania, and the 

Southern Appalachians ecoregion, which extends 

from Pennsylvania into Alabama, through the 

eastern portion of the Ohio Valley, and includes 

the Ozark Mountains of Missouri, Arkansas, and 

Oklahoma. 

Figure 8. Nine ecoregions were surveyed for the WSA (U.S. EPA/WSA).

WSA Ecological Regions*

Northern Appalachians Southern Plains

Southern Appalachians Northern Plains

Coastal Plains Western Mountains

Upper Midwest Xeric

Temporate Plains *based on Omernik Level III ecoregions
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Chapter 1 Design of the Wadeable Streams Assessment

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The Plains and Lowlands region includes fi ve 

WSA ecoregions: the Coastal Plains, the Upper 

Midwest, the Temperate Plains, the Northern 

Plains, and the Southern Plains. The Coastal Plains 

ecoregion covers the low-elevation areas of the East 

and Southeast, including the Atlantic and Gulf 

of Mexico coastal plains and the lowlands of the 

Mississippi Delta, which extend from the Gulf of 

Mexico northward through Memphis, TN. The 

Upper Midwest ecoregion is dominated by lakes 

and has little elevation gradient. The Temperate 

Plains ecoregion in the midwestern United States 

is probably most well-known as the Cornbelt. The 

Northern Plains and Southern Plains ecoregions 

are better known as the Great Prairies, with the 

Northern Plains ecoregion encompassing North 

Dakota, South Dakota, Montana, and northeast 

Wyoming, and the Southern Plains ecoregion 

encompassing parts of Nebraska, Kansas, Colorado, 

New Mexico, Oklahoma, and Texas. 

The West region includes two WSA ecoregions: 

the Western Mountains ecoregion and the arid or 

Xeric ecoregion. The Western Mountains ecoregion 

includes the Cascade, Sierra Nevada, and Pacifi c 

Coast mountain ranges in the coastal states; the 

Gila Mountains in the southwestern states; and the 

Bitteroot and Rocky Mountains in the northern 

and central mountain states. The Xeric ecoregion 

includes both the true deserts and the arid lands of 

the Great Basin.

Some states participating in the WSA assessed 

an even fi ner state-scale resolution than the 

ecoregion scale by sampling additional random sites 

within their state borders. Although these data are 

included in the analysis described in this report, 

state-scale results are not presented for each state. 

These states are preparing similar analyses that 

refl ect their respective water quality standards and 

regulations.

How Were Sampling Sites 

Chosen?

The WSA sampling locations were selected 

using modern survey design approaches. Sample 

surveys have been used in a variety of fi elds (e.g., 

election polls, monthly labor estimates, forest 

inventory analyses, National Wetlands Inventory) 

to determine the status of populations or 

resources of interest using a representative sample 

of a relatively few members or sites. This approach 

is especially cost effective if the population is so 

large that all components cannot be sampled or 

if obtaining a complete census of the resource is 

unnecessary to reach the desired level of precision 

for describing conditions. 

Survey data are frequently reported in the 

news. For example, the percentage of children 

1–5 years old living in the United States who 

have high lead levels in their blood is 2.2% +/- 

1.2%, an estimate based on a random sample of 

children in the United States. The WSA results 

have similar rigor in their ability to estimate the 

percentage of stream miles, within a range of 

certainty, that are in good condition. 

To pick a random sample, the location of 

members of the population of interest must 

be known. The target population for the WSA 

was the wadeable, perennial streams in the 

conterminous United States. The WSA design 

team used the National Hydrography Dataset 

(NHD)—a comprehensive set of digital spatial 

data on surface waters—to identify the location of 

wadeable, perennial streams. They also obtained 

information about stream order from the River 

Reach File, a related series of hydrographic 

databases that provide additional attributes about 

stream reaches. Using these resources, researchers 

determined the length of wadeable streams for 

each of the nine ecoregions (Figure 9).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

16

 For this WSA report, the wadeable stream miles 

assessed for the nation, regions, and ecoregions are 

referred to as the stream length. The total stream 

length represented in the WSA for the nation is 

671,051 miles. For the Eastern Highlands, Plains 

and Lowlands, and West regions, the total stream 

length assessed for the WSA is 276,362 miles, 

242,264 miles, and 152,425 miles, respectively. 

The 1,392 sites sampled for the WSA were 

identifi ed using a particular type of random 

sampling technique called a probability-based 

sample design, in which every element in the 

population has a known probability of being 

selected for sampling. This important feature 

ensures that the results of the WSA refl ect the full 

range in character and variation among wadeable 

streams across the United States. Rules for site 

selection included weighting to provide balance 

in the number of stream sites from each of the 

1st- through 5th-order size classes and controlled 

spatial distribution to ensure that sample sites were 

distributed across the United States (Figure 10).

The WSA sites were allocated by EPA Region 

and WSA ecoregion based on the distribution 

of 1st- through 5th-order streams within those 

regions. Within each EPA Region, random sites 

are more densely distributed where the perennial 

1st- through 5th-order streams are more densely 

located and more sparsely distributed where 

streams are sparse. For example, EPA Region 4 

in the southeastern United States includes large 

portions of the Southern Appalachian and Coastal 

Plains ecoregions. The survey design in EPA 

Region 4 identifi ed more sites in the Southern 

Appalachians ecoregion, where the stream length 

is 178,449 miles, than in the Coastal Plains 

ecoregion, where the stream length is 72,130 

miles (see Figure 9). 

 The basic sampling design drew 50 sampling 

sites randomly distributed in each of the EPA 

Regions and WSA ecoregions. Some of the 

unusually dense site patterns visible on Figure 

10 occur because some states opted to increase 

the intensity of random sampling throughout 

National 671,051

(lower 48)

Southern Appalachian 178,449

Western Mountains 126,436

Temperate Plains 100,879

Northern Appalachians 97,913

Coastal Plains 72,130

Upper Midwest 36,547

Xeric 25,989

Southern Plains 19,263

Northern Plains 13,445

0 200,000 400,000 600,000 800,000

Figure 9. Length of wadeable, perennial streams in each WSA ecoregion (U.S. EPA/WSA).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Figure 10. Sites sampled for the WSA by EPA Region (U.S. EPA/WSA).

Chapter 1 Design of the Wadeable Streams Assessment

17

their state to characterize statewide conditions. 

Fifteen states, including all states in EPA 

Regions 8, 9, and 10, increased the number of 

random sites to 50 sites throughout each state 

to support state-scale characterizations of stream 

condition. States also added clusters of random 

sites to characterize areas of special interest in 

Washington, Oregon, and California. When sites 

from an area of intensifi cation were used in the 

ecoregion assessments, the weights associated with 

those sites were adjusted so that the additional 

sites did not dominate the results. The unbiased 

site selection of the survey design ensures that 

assessment results represent the condition of the 

streams throughout the nation.

An additional 150 reserve replacement sites 

were generated for each of the 10 EPA Regions. 

These replacement sites were used when site 

reconnaissance activities documented that one of 

the original stream sites could not be sampled. For 

example, sites were replaced when a waterbody 

did not meet the defi nition of a wadeable stream 

(e.g., no fl owing water over 50% of the reach) or 

was unsafe for sampling, or when access to the 

stream was denied by the landowner. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

18

Highlight

WSA Sampling Frame

The basis of the WSA target population is 1st- through 5th-order perennial streams, which are 

the streams most likely to be wadeable. The sampling frame used to represent the target population 

and to select the sites for the WSA is based on the perennial stream network contained in the 

USGS-EPA NHD. The NHD is a digitized version of 1:100K USGS topographic maps and shows 

both perennial and non-perennial (e.g., intermittent and ephemeral) streams.

The total stream length in the NHD stream and river network labeled perennial in the 

conterminous United States is 1,204,859 miles. Of this amount, 1,131,062 miles are 1st- through 

4th-order streams, which make up 91% of the total stream length of the nation’s fl owing waters (see 

fi gure below).

Of the more than 1 million miles of stream length labeled as perennial, almost 34% (400,000 

miles) were found to be non-perennial or non-target waterbodies (e.g., wetlands, reservoirs, 

irrigation canals). The remaining target stream length represents the portion of the NHD that 

meets criteria for inclusion in the WSA (e.g., perennial, wadeable streams). A portion of that target 

stream length was not sampled for various reasons, including denial of access by a landowner or 

inaccessibility.

In addition to generating results on the condition of perennial streams, the WSA provides data on 

the total length of perennial stream miles in the United States. These results will be loaded into the 

NHD so that the database is updated on the status of perennial/non-perennial stream information.

0 300,000 600,000 900,000 1200,000 1,500,000

Length (miles)

Total NHD Length 1,240,849

1st – 4th Order 1,131,062 (91%)

5th Order 59,409 (5%)

6th Order 12,063 (1%)

7th Order 31,850 (3%)

8th Order 6,342 (<1%)

Estimate of perennial length of streams and rivers from the NHD (U.S. EPA/WSA). 

The 1st- through 4th-order streams comprise 91% of total estimated stream length in the NHD. 

The 1st- through 5th-order streams form the basis for the sampling design frame for the WSA. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

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 How Were Waters Assessed?

Each WSA site was sampled by a two- to fourperson fi eld crew between 2000 and 2004 during 

a summer index period. More than 40 trained 

crews, comprised primarily of state environmental 

staff, sampled 1,392 stream sites using 

standardized fi eld protocols. The fi eld protocols 

were designed to consistently collect data relevant 

to the biological condition of stream resources 

and the resources’ key stressors.

During each site visit, crews laid out the 

sample reach and the numerous transects to 

guide data collection (Figure 11). Field crews 

sent water samples to a laboratory for basic 

chemical analysis, whereas biological samples 

collected from 11 transects along each stream 

reach were sent to taxonomists for identifi cation 

of macroinvertebrates. Crews also completed 

roughly 35 pages of fi eld forms, recording data 

and information about the physical characteristics 

Figure 11. Reach layout for sampling (U.S. EPA/WSA).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

20

of each stream and the riparian area adjacent to 

its banks. Each crew was audited, and 10% of the 

sites were revisited as part of the quality assurance 

plan for the survey. 

The use of standardized fi eld and laboratory 

protocols for sampling is a key feature of the 

WSA. Because ecologists use a range of methods 

to sample streams, it is often diffi cult to compare 

data collected by different states, regions, 

or agencies on a regional or national level. 

Standardization allows the data to be combined 

to produce a nationally consistent assessment. In 

addition to collecting a national set of consistent 

data, this nationwide sampling effort provided 

an opportunity to examine the comparability of 

different sample protocols by applying both the 

WSA method and various state or USGS methods 

to a subset of the sites. A separate analysis is 

underway to examine the comparability of 

these methods and explore options for how the 

resulting data may be used together.

The WSA uses benthic macroinvertebrates 

(e.g., aquatic larval stages of insects, crustaceans, 

worms, mollusks) as the biological indicator 

of a stream’s ecological condition. Benthic 

macro inv ertebrates live throughout the stream 

bed, attaching to rocks and woody debris and 

burrowing in sandy stream bottoms and among 

the debris, roots, and grasses that collect and 

grow along the water’s edge (Figure 12). The 

Figure 12. Stream macroinvertebrates (Photo courtesy of Maine Department of Environmental 

Protection). Macroinvertebrates in streams serve as the basis for the indicators of biological condition 

for the WSA.

Stonefl ies

Dragonfl ies,

Damselfl ies

Beetles

Mayfl ies

Caddisfl ies

Midges
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

21

WSA focuses on these macroinvertebrates 

because of their inherent capacity to integrate 

the effects of the stressors to which they are 

exposed, in combination and over time. Stream 

macroinvertebrates generally cannot move very 

quickly or very far; therefore, they are affected by, 

and may recover from, a number of changes in 

physical conditions (e.g., habitat loss), chemical 

conditions (e.g., excess nutrients), and biological 

conditions (e.g., the presence of invasive or nonnative species). Some types of macroinvertebrates 

are affected by these conditions more than others.

Macroinvertebrates provide a measurement 

of biological condition or health relative to 

the biological integrity of a stream. Biological 

integrity represents the capability of supporting 

and maintaining a balanced, integrated, 

adaptive community of organisms having a 

species composition, diversity, and functional 

organization comparable to that of the natural 

habitat of the region. Macroinvertebrates are 

researched by almost every state and federal 

program that monitors streams and are also 

increasingly evaluated by volunteer organizations 

that monitor water quality. In addition, water 

quality monitoring and management programs 

are enhancing the understanding of the biological 

condition of streams by adding other biological 

assemblages, including fi sh and algae.

The WSA supplements information on 

the biological condition of streams with 

measurements of key stressors that might 

negatively infl uence or affect stream condition. 

Stressors are the chemical, physical, and biological 

components of the ecosystem that have the 

potential to degrade stream biology. Some 

stressors are naturally occurring, whereas others 

result only from human activities, although most 

come from both sources. 

Most physical stressors are created when we 

modify the physical habitat of a stream or its 

watershed, such as through extensive urban or 

agricultural development, excessive upland or 

bank erosion, or loss of streamside trees and 

vegetation. Examples of chemical stressors include 

toxic compounds (e.g., heavy metals, pesticides), 

excess nutrients (e.g., nitrogen and phosphorus), 

or acidity from acidic deposition or mine 

drainage. Biological stressors are characteristics of 

the biota that can infl uence biological integrity, 

such as the proliferation of non-native or invasive 

species (either in the streams and rivers, or in the 

riparian areas adjacent to these waterbodies). 

The WSA water chemistry data allow an 

evaluation of the distribution of nutrients, 

salinity, and acidifi cation in U.S. streams. The 

physical habitat data provide information on the 

prevalence of excess sediments, the quality of 

in-stream fi sh habitat, and the quality of riparian 

habitat alongside streams. Although these are 

among the key stressors identifi ed by states as 

affecting water quality, they do not refl ect the full 

range of potential stressors that can impact water 

quality. Future water quality surveys will include 

an assessment of additional stressors.

One of the key components of an ecological 

assessment is a measure of how important (e.g., 

how common) each stressor is within a region 

and how severely it affects biological condition. 

In addition to looking at the extent of streams 

affected by key stressors, the WSA evaluated the 

relative risk posed by key stressors to biological 

condition.
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Chapter 1 Design of the Wadeable Streams Assessment

22

Highlight

Understanding Biological Condition

The main goal of the WSA is to develop a baseline understanding of the biological condition of 

our nation’s streams. Why is this important?

One of the most meaningful ways to answer basic questions about water quality is to directly 

observe the communities of plants and animals that live in waterbodies. Aquatic plants and 

animals—especially the small creatures that are the focus of this study—are constantly exposed 

to the effects of various stressors; therefore, they refl ect not only current conditions, but also the 

cumulative impacts of stresses and changes in conditions over time. 

Benthic macroinvertebrates are widely used to determine biological condition. These organisms 

can be found in all streams, even in the smallest streams that cannot support fi sh. Because they 

are relatively stationary and cannot escape pollution, macroinvertebrate communities integrate the 

effects of stressors over time (i.e., pollution-tolerant species will survive in degraded conditions, 

and pollution-intolerant species will die). These communities are also critically important to fi sh 

because most game and non-game species require a good supply of benthic macroinvertebrates 

as food. Biologists have been studying the health and composition of benthic macroinvertebrate 

communities in streams for decades.

Biological condition is the most comprehensive indicator of waterbody health; when the biology 

of a stream is healthy, the chemical and physical components of the stream are also typically in 

good condition. In fact, several states have found that biological data frequently detect stream 

impairment where chemistry data do not.

Data on biological condition are invaluable for managing the nation’s aquatic resources and 

ecosystems. Water quality managers can use these data to set protection and restoration goals, 

decide which indicators to monitor and how to interpret monitoring results, identify stresses 

to the waterbody and decide how they should be controlled, and assess and report on the 

effectiveness of management actions. In fact, many specifi c state responsibilities under the CWA—

such as determining the extent to which waters support aquatic life uses, evaluating cumulative 

impacts from polluted runoff, and determining the effectiveness of discharger permit controls—are 

tied directly to an understanding of biological condition. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

23

Setting Expectations

To interpret the data collected and assess 

current ecological condition, chemical, physical, 

and biological measurements must be compared 

to a benchmark or estimate of what one would 

expect to fi nd in a natural condition. Setting 

reasonable expectations for an indicator is one of 

the greatest challenges to making an assessment of 

ecological condition. Should we take an historical 

perspective and try to compare current conditions 

to an estimate of pre-colonial conditions, preindustrial conditions, or conditions at some other 

point in history, or should we accept that some 

level of anthropogenic disturbance is expected 

and simply use the best of today’s conditions as 

the benchmark against which everything else is 

compared?

These questions, and their answers, all relate 

to the concept of reference condition. What 

do we use as a reference condition to set the 

benchmark for assessing the current status of 

these waterbodies? Because of the diffi culty of 

estimating historical conditions for many of 

the WSA indicators, the assessment used the 

conditions at a collection of “least-disturbed” 

sites as the reference condition. This means 

that the condition at these sites represents the 

best available chemical, physical, and biological 

habitat conditions given the current state of the 

landscape. Least-disturbed sites were identifi ed 

by evaluating data collected at sites according to a 

set of explicit screening levels that defi ne what is 

least disturbed by human activities. To refl ect the 

natural variability across the American landscape, 

these levels varied among the nine ecoregions. 

The WSA compared physical and chemical data 

collected at each site (e.g., nutrients, riparian 

condition, chloride, turbidity, fi ne sediments) 

to the screening levels to determine whether any 

given site was in least-disturbed condition for its 

ecoregion.

Data on land use in the watersheds were not 

used to screen-out sites. For example, sites in 

agricultural areas with effective best management 

practices (BMPs) may have been considered least 

disturbed, provided they exhibited chemical and 

physical conditions that were among the best 

for their region. The WSA also did not use data 

on biological assemblages as a screening factor 

to select reference sites because that would have 

pre-judged expectations for biological condition. 

Similarly, when selecting least-disturbed reference 

sites for each stressor, the WSA excluded the 

specifi c stressors themselves from the screening 

process. 

The WSA screening process resulted in the 

identifi cation of a set of least-disturbed reference 

sites for each WSA ecoregion. These sites were 

distributed throughout the ecoregions and 

A researcher collects macroinvertebrate samples 

from a small stream in the Northern Appalachians

ecoregion (Photo courtesy of the Vermont Department

of Environmental Conservation).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 1 Design of the Wadeable Streams Assessment

24

covered the range of natural variability across 

each area. Some of these sites included a degree of 

human-caused variability.

The results from samples collected at the 

reference sites for the various indicators (e.g., 

biological condition, nutrients) represent the 

range of expected values for least-disturbed 

reference condition. The WSA used this reference 

distribution as a benchmark for setting thresholds 

between good, fair, and poor condition. These 

thresholds were then applied to the random sites 

to generate the percentage of stream length in 

each condition class.

The WSA’s approach examined the range 

of values for indicators in all of the reference 

sites in a region and used the 5th percentile of 

the reference distribution for that indicator to 

separate the poor sites from fair sites. Using 

the 5th percentile means that stream sites and 

associated stream length in poor condition 

were worse than 95% of the sites used to defi ne 

least-disturbed reference condition. Similarly, 

the 25th percentile of the reference distribution 

was used to distinguish between sites in fair and 

good condition. This means that stream length 

reported as being in good condition was as good 

as or better than 75% of the sites used to defi ne 

least-disturbed reference condition.

Within the reference site population, there 

exist two sources of variability: natural variability 

and variability due to human activities. Natural 

variability—the wide range of habitat types 

naturally found within each ecoregion—creates 

a spread of reference sites representing these 

differing habitats. Capturing natural variability in 

reference sites helps establish reference conditions 

that represent the range of environments in the 

ecoregions. 

The second source of variation within the 

reference population is change resulting from 

human activities. Many areas in the United 

States have been altered, with natural landscapes 

transformed by cities, suburban sprawl, 

agricultural development, and resource extraction. 

The extent of those disturbances varies across 

regions. Some of the regions of the country have 

reference sites in watersheds with little to no 

evidence of human impact, such as mountain 

streams or streams in areas with very low 

population densities. Other regions of the country 

have few sites that have not been infl uenced by 

human activities. The least-disturbed reference 

sites in these widely infl uenced watersheds 

display more variability in quality than those in 

watersheds with little human disturbance. 

Variation within the reference distribution due 

to disturbance was addressed before benchmarks 

were set for the condition classes of good, fair, 

and poor. For regions where the reference sites 

exhibited a disturbance signal, the data analysis 

team accounted for this disturbance by shifting 

the mean of the distribution toward the lessdisturbed reference sites. 

At a national meeting to discuss data analysis 

options, WSA collaborators supported this 

reference condition-based approach, which is 

consistent with EPA guidance and state practice 

on the development of biological and nutrient 

criteria. Additional details on how the leastdisturbed condition and benchmarks for the 

condition categories were established for the 

WSA can be found in the data analysis method 

available on the EPA Web site at http://www.epa.

gov/owow/streamsurvey. 
Chapter 2

Condition of the Nation’s 

Streams

Photo courtesy of the Georgia Department of Natural Resources
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

26

Chapter 2 Condition of the Nation’s Streams

Condition of the

Nation’s Streams

Background

The CWA explicitly aims “to restore and 

maintain the chemical, physical, and biological 

integrity of the nation’s waters.” The WSA 

examines these three aspects of water quality 

through a small set of commonly used and widely 

accepted indicators. Although this WSA report 

does not include all aspects of biological integrity 

or review all possible chemical, physical, or 

biological stressors known to affect water quality, 

it does present the results of important indicators 

for an entire class of water resources—wadeable, 

perennial streams.

This chapter describes the results of the WSA 

and is organized as follows:

• Indicators of Biological Condition – Provides 

a description of the indicators or attributes of 

biological condition that were measured by the 

WSA survey and the results of the data analysis. 

• Aquatic Indicators of Stress – Presents 

fi ndings on the stressors evaluated for the 

study. 

• Ranking of Stressors – Presents an analysis 

of the relative importance of the stressors in 

affecting biological condition.

Results for each indicator are shown for the 

nation’s streams and for the three major regions 

(Eastern Highlands, Plains and Lowlands, and 

West). Chapter 3 of this report presents indicator 

results for each of the nine WSA ecoregions. 

Indicators of Biological 

Condition

Ecologists evaluate the biological condition of 

water resources, including wadeable streams, by 

analyzing key characteristics of the communities 

of organisms that live in these waterbodies. 

These characteristics include the composition 

and relative abundance of key groups of animals 

(e.g., fi sh and invertebrates) and plants (e.g., 

periphyton, or algae that attach themselves 

to stream bottoms, rocks, and woody debris) 

Jellison Meadow Brook, ME, in the Eastern Highlands region

(Photo courtesy of Colin Hill, Tetra Tech, Inc.).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

27

What are Taxa?

Taxa (plural of taxon) are groupings of living 

organisms, such as phylum, class, order, family, genus, 

or species. Biologists scientifi cally describe and 

organize organisms into taxa in order to better 

identify and understand them.

found in streams. The WSA focused on just one 

assemblage, benthic macroinvertebrates (e.g., 

aquatic insects, crustaceans, worms and mollusks); 

however, some WSA participants also researched 

other assemblages.

Why focus on macroinvertebrates? Macroinvertebrates are key organisms that refl ect the 

quality of their environment and respond to 

human disturbance in fairly predictable ways. 

As all fl y-fi shermen know, the insects emerging 

from streams and rivers are good indicators of 

the water quality and serve as an important 

food source for both game and non-game fi sh. 

Given the wide geographic distribution of 

macroinvertebrates, as well as their abundance 

and link to fi sh and other aquatic vertebrates, 

these organisms serve as excellent indicators of the 

quality of fl owing waters and the human stressors 

that affect these systems.

WSA researchers collected samples of these 

organisms and sent them to laboratories for 

analysis, yielding a data set that provided the 

types and number of taxa (i.e., classifi cations 

or groupings of organisms) found at each 

site. To interpret this data set, the WSA used 

two indicators of biological condition: the 

Macroinvertebrate Index of Biotic Condition and 

the Observed/Expected (O/E) Ratio of Taxa Loss.

Macroinvertebrate Index

of Biotic Condition

The Macroinvertebrate Index of Biotic 

Condition (henceforth referred to as the 

Macroinvertebrate Index) is similar in concept 

to the economic Consumer Confi dence Index 

(or the Leading Index of Economic Indicators) 

in that the total index score is the sum of 

scores for a variety of individual measures, also 

called indicators or metrics. To determine the 

Leading Index, economists look at a number of 

metrics, including manufacturers’ new orders 

for consumer goods, building permits, money 

supply, and other aspects of the economy that 

refl ect economic growth. To determine the 

Macroinvertebrate Index, ecologists look at such 

metrics as taxonomic richness, habit and trophic 

composition, sensitivity to human disturbance, 

and other biotic aspects that refl ect “naturalness.” 

Originally developed as an Index of Biotic 

Integrity for fi sh in Midwestern streams, the 

Macroinvertebrate Index has been modifi ed and 

applied to other regions, taxonomic groups, and 

ecosystems.

The metrics used to develop the Macroinvertebrate Index for the WSA covered six 

different characteristics of macroinvertebrate 

assemblages that are commonly used to evaluate 

biological condition: 

• Taxonomic richness – This characteristic 

represents the number of distinct taxa, or 

groups of organisms, identifi ed within a 

sample. Many different kinds of distinct taxa, 

particularly those that belong to pollutionsensitive insect groups, indicate a variety of 

physical habitats and food sources and an 

environment exposed to generally lower levels 

of stress.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

28

Chapter 2 Condition of the Nation’s Streams

Highlight

Using Multiple Biological Assemblages to Determine Biological Condition

EPA’s guidance on developing biological assessment and criteria programs recommends the 

use of multiple biological assemblages to determine biological condition. The term “multiple 

biological assemblages” simply refers to the three main categories of life found in a waterbody: 

plants (e.g., algae), macroinvertebrates, and vertebrates (e.g., fi sh). The purpose of examining 

multiple biological assemblages is to generate a broader perspective of the condition of the 

aquatic resource of interest. 

Each assemblage plays a different role in the way that rivers and streams function. Algae 

and macroinvertebrates occur throughout all types and sizes of streams, whereas very small 

streams may be naturally devoid of fi sh. Algae are the base of the food chain and capture 

light and nutrients to generate energy. They are sensitive to changes in shading, turbidity, and 

increases or decreases in nutrient levels. Macroinvertebrates feed on algae and other organic 

material that enters the aquatic system from the surrounding watershed. Macroinvertebrates 

also form the base of the food chain for many aquatic vertebrates. Fish are an example of 

these aquatic vertebrates and also serve as an important food source for people and wildlife. 

Each of these groups of aquatic organisms is sensitive in its own way to different humaninduced disturbances. 

The WSA collaboration began as a partnership among 12 western states; EPA Regions 8, 

9, and 10; and EPA’s Western Ecology Division (Environmental Monitoring and Assessment 

Program [EMAP] West) before it was expanded to include the entire United States. The 

original EMAP West program addressed fi sh, macroinvertebrates, and algae; future WSA reports 

will also address multiple assemblages.

To learn more about EMAP West and its use of multiple biological assemblages, visit www.

epa.gov/emap/west/index.html.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

29

• Taxonomic composition – Ecologists 

calculate composition metrics by identifying 

the different taxa groups, determining which 

taxa in the sample are ecologically important, 

and comparing the relative abundance of 

organisms in those taxa to the whole sample. 

Healthy stream systems have organisms from 

across many different taxa groups, whereas 

unhealthy stream systems are often dominated 

by a high abundance of organisms in a small 

number of taxa that are tolerant of pollution.

• Taxonomic diversity – Diversity metrics look 

at all the taxa groups and the distribution 

of organisms among those groups. Healthy 

streams should have a high level of diversity 

throughout the assemblage. 

• Feeding groups – Many macroinvertebrates 

have specialized strategies to capture and 

process food from their aquatic environment. 

As a stream degrades from its natural 

condition, the distribution of animals among 

the different feeding groups will change. For 

example, as a stream loses its canopy (a source 

of leaves and shading), the aquatic community 

will shift from a more diverse food chain to 

one of predominantly algal-feeding animals 

that are tolerant of warm water. 

• Habits – Just like other organisms, benthic 

macroinvertebrates are characterized by 

certain habits, including how they move and 

where they live. These habits are captured 

in the habit metrics. For example, some 

taxa burrow under the streambed sediment, 

whereas others cling to rocks and debris within 

the stream channel. A stream that naturally 

includes a diversity of habitat types will 

support animals with diverse habits; however, 

if a stream becomes laden with silt, the 

macroinvertebrates that cling, crawl, and swim 

will be replaced by those that burrow. 

• Pollution tolerance – Each macroinvertebrate 

taxa can tolerate a specifi c range of stream 

contamination, which is referred to as 

their pollution tolerance. Once this level is 

exceeded, the taxa are no longer present in that 

area of the stream. Highly sensitive taxa, or 

those with a low pollution tolerance, are found 

only in streams with good water quality. 

The specifi c metrics chosen for each of these 

categories varied among the nine ecoregions used 

in the analysis. Each metric was scored and then 

combined to create an overall Macroinvertebrate 

Index for each region, with values ranging from 

0 to 100. For the WSA, analysts calculated a 

Macroinvertebrate Index score for each site, 

factored in the stream length represented by the 

site, and then generated an estimate of the stream 

length in a region, and nationally, with a given 

Macroinvertebrate Index score.

Six different characteristics of macroinvertebrate 

assemblages are commonly used to evaluate 

biological condition in wadeable streams (Photo 

courtesy of Lauren Holbrook, IAN Image Library).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

30

Chapter 2 Condition of the Nation’s Streams

Findings for the Macroinvertebrate Index 

of Biotic Condition

As illustrated in Figure 13, the Macroinvertebrate Index indicator results show that 42% of 

the nation’s stream length (281,170 miles) is 

in poor condition, 25% (167,092 miles) is in 

fair condition, and 28% (189,236 miles) is in 

good condition compared to the least-disturbed 

reference condition in each of the nine WSA 

ecoregions. The 28% of stream length in good 

condition has conditions most similar to the 

reference distribution derived from the bestavailable (least-disturbed) sites in each ecoregion. 

The 5% (33,553 miles) of unassessed stream 

length results from the fact that 1st-order streams 

in New England were not sampled for the WSA.

Macroinvertebrate Index results show that 

the Eastern Highlands region has the highest 

proportion of stream length (52%, or 143,170 

miles) in poor condition, followed by the Plains 

and Lowlands (40%, or 96,905 miles) and the 

West (27%, or 41,754 miles). 

Figure 13. Biological condition of streams based on Macroinvertebrate Index of Biotic Condition

(U.S. EPA/WSA). The Macroinvertebrate Index combines metrics of benthic community structure and function 

into a single index for each region. The thresholds for defi ning good, fair, and poor condition were developed for 

each of the nine WSA ecoregions based on condition at the least-disturbed reference sites. Stream length in good 

condition is most similar to least-disturbed reference condition; in fair condition has Macroinvertebrate Index 

scores worse than 75% of reference condition; and in poor condition has Macroinvertebrate Index scores worse 

than 95% of reference condition.

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60

Percentage of Stream Miles

Stream Length (mi)

68,672

39,403

41,754

2,596

Total: 152,425

29.0% 70,257

29.0% 70,257

40.0% 96,905

4,845

Total: 242,264

45.1%

25.8%

27.4%

28.2% 189,236

24.9% 167,092

41.9% 281,170

33,553

Total: 671,051

5.0%

18.2% 50,320

20.5% 56,501

51.8% 143,170

26,371

Total: 276,362

9.5%

G

F

P

N/A

G

F

P

N/A

G

F

P

N/A 2.0%

G

F

P

N/A

Good Fair Poor Not Assessed

1.7%
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

31

What are Confi dence Intervals?

Confi dence intervals (i.e., the small lines at the end of the bars in this report’s charts) are provided to convey the 

level of certainty or confi dence that can be placed in the information presented in this report. For example, for the 

national Macroinvertebrate Index, the WSA fi nds that 28.2% of the nation’s stream length is in good condition, and the 

confi dence is +/- 2.8%, which means that there is a 95% certainty that the real value is between 25.4% and 31%. The 

confi dence interval depends primarily on the number of sites sampled; as more streams are sampled, the confi dence 

interval becomes narrower, meaning there is more confi dence in the fi ndings. When fewer streams are sampled, the 

confi dence interval become broader, meaning there is less certainty in the fi ndings. Figure 13 shows an example of this 

pattern, in which the confi dence interval for the national results (the largest sample size) is narrowest, whereas the 

confi dence intervals for the major regions, where a smaller number of streams were sampled, are generally broader. 

Ultimately the breadth of the confi dence interval is a tradeoff between the need for increased certainty to support 

decisions and the money and resources dedicated to monitoring.

Macroinvertebrate Observed/

Expected (O/E) Ratio of Taxa 

Loss

The Macroinvertebrate O/E Ratio of Taxa 

Loss (henceforth referred to as O/E Taxa Loss) 

measures a specifi c aspect of biological health: 

taxa that have been lost at a site. The taxa 

expected (E) at individual sites are predicted 

from a model developed from data collected at 

least-disturbed reference sites; thus, the model 

allows a precise matching of sampled taxa with 

those that should occur under specifi c, natural 

environmental conditions. By comparing the list 

of taxa observed (O) at a site with those expected 

to occur, the proportion of expected taxa that 

have been lost can be quantifi ed as the ratio of O/

E. Originally developed for streams in the United 

Kingdom, O/E Taxa Loss models are modifi ed 

for the specifi c natural conditions in each area 

for which they are used. The O/E Taxa Loss 

indicator is currently used by several countries 

and numerous states in the United States.

O/E Taxa Loss values range from 0 (none of 

the expected taxa are present) to slightly greater 

than 1 (more taxa are present than expected). 

These values are interpreted as the percentage of 

the expected taxa present. Each tenth of a point 

less than 1 represents a 10% loss of taxa at a site; 

thus, an O/E Taxa Loss score of 0.9 indicates 

that 90% of the expected taxa are present and 

10% are missing. O/E Taxa Loss values must 

be interpreted in the context of the quality of 

reference sites used to build the predictive models, 

because the quality of reference sites available in 

a region sets the bar for what is expected (i.e., 

regions with lower-quality reference sites will 

have a lower bar). Although an O/E Taxa Loss 

value of 0.8 means the same thing regardless of 

a region (i.e., 20% of taxa have been lost relative 

to reference conditions in each region), the true 

amount of taxa loss will be underestimated if 

reference sites are of low quality.

The WSA developed three O/E Taxa Loss 

models to predict the extent of taxa loss across 

streams of the United States, one model for each 

of the three major regions outlined in this report 

(Eastern Highlands, Plains and Lowlands, West). 

Analysts used the O/E Taxa Loss scores observed 

at each site to generate estimates of the nation’s 

stream length estimated to fall into four categories 

of taxa loss. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

32

Chapter 2 Condition of the Nation’s Streams

Although in many cases the results of O/E 

Taxa Loss analysis are similar to the results of the 

Macroinvertebrate Index, such agreement will 

not always occur. The O/E Taxa Loss indicator 

examines a specifi c aspect of biological condition 

(biodiversity loss), whereas the Macroinvertebrate 

Index combines multiple characteristics. For 

the WSA, the two indicators provided similar 

results in those WSA ecoregions that had a lower 

disturbance signal among their reference sites.

Findings for O/E Taxa Loss

Figure 14 displays the national and regional 

O/E Taxa Loss summary. These data are presented 

in four categories: (1) less than 10% taxa loss,

(2) 10–20% taxa loss, (3) 20–50% taxa loss, and 

(4) more than 50% taxa loss. Forty-two percent 

of the nation’s stream length retained more than 

90% of expected taxa; 13% lost 10–20% of taxa; 

26% lost 20–50% of taxa; and 13% lost more 

than 50% of taxa. 

Within the three regions, stream length in 

the Eastern Highlands experienced the greatest 

loss of expected taxa, with 17% experiencing 

a loss of 50% or more. An additional 29% of 

stream length in this region lost 20–50% of 

taxa; 13% lost 10–20% of taxa; and only 28% 

of stream length lost fewer than 10% of taxa. 

Eleven percent of stream length in the Plains and 

Lowlands region experienced a taxa loss of 50% 

or more, 25% of stream length lost 20–50% of 

National

(lower 48)

Eastern Highlands

Plains and Lowlands

West

0 10 20 30 40 50 60 70 80 90 100

Percentage of Stream Miles

96.4%

> 50% Taxa Loss 20–50% Taxa Loss

10–20% Taxa Loss < 10% Taxa Loss Not Assessed

12.6% 26.0% 12.5% 41.5% 7.4%

16.8% 29.1% 13.4% 27.9% 12.8%

11.3% 25.0% 13.3% 47.0% 3.4%

6.9% 21.2% 9.6% 57.9% 4.4%

Figure 14. Macroinvertebrate taxa loss as measured by the O/E Ratio of Taxa Loss (U.S. EPA/WSA). 

The O/E Taxa Loss indicator displays the loss of taxa from a site compared to reference for that region. 

Scores 0.1 lower than reference represent a 10% loss in taxa.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

33

taxa; 13% lost 10–20% of taxa; and 47% lost 

fewer than 10% of taxa. In the West, 7% of 

stream length experienced a taxa loss of 50% or 

more, 21% of stream length lost 20–50% of taxa; 

10% lost 10–20% of taxa; and 58% of stream 

length lost less than 10% of taxa.

Aquatic Indicators of Stress

As people use the landscape, their actions 

can produce effects that are stressful to aquatic 

ecosystems. These aquatic stresses can be 

chemical, physical, or in some cases, biological. 

The WSA has selected a short list of stressors 

from each of these categories as indicators for 

assessment. This list is not intended to be allinclusive, and in fact, some important stressors 

are not included because there is currently no 

way to assess them at the site scale (e.g., water 

withdrawals for irrigation). Future assessments 

of U.S. stream and river condition will include a 

more comprehensive list of stressors from each of 

these categories.

WSA indicators are based on direct measures 

of stress in the stream or adjacent riparian areas, 

not on land use or land cover alterations, such 

as row crops, mining, or grazing. Many human 

activities and land uses can be sources of one 

or more stressors to streams; however, the WSA 

only assesses stressors to determine the general 

condition of the resource and which stressors are 

most signifi cant and does not track the source of 

these stressors. Source tracking, an expensive and 

time-consuming process, is a logical future step 

for the WSA and similar national assessments.

A summary of the national and regional results 

for indicators of chemical and physical habitat 

are shown in Figures 15 through 22. WSA results 

for these indicators for each of the nine WSA 

ecoregions are presented in Chapter 3 of this 

report. 

Chemical Stressors

Four chemical stressors were assessed as 

indicators in the WSA: total phosphorus, total 

nitrogen, salinity, and acidifi cation. These 

stressors were selected because of national or 

regional concerns about the extent to which 

each might be impacting the quality of stream 

biota. The thresholds for interpreting data were 

developed from a set of least-disturbed reference 

sites for each of the nine WSA ecoregions, as 

described in Chapter 1, Setting Expectations. The 

results for each ecoregion were tallied to report 

on conditions for the three major regions and the 

entire nation.

Total Phosphorus Concentrations

Phosphorus is usually considered the most 

likely nutrient limiting algal growth in U.S. 

freshwater waterbodies. Because of the naturally 

low concentrations of phosphorus in stream 

systems, even small increases in phosphorus 

concentrations can impact a stream’s water 

quality. Some waters—such as streams originating 

from groundwater in volcanic areas of eastern 

Oregon and Idaho—have naturally higher 

concentrations of phosphorus. This natural 

variability is refl ected in the regional thresholds 

for high, medium, and low, which are based on 

the least-disturbed reference sites for each of the 

nine WSA ecoregions. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

34

Chapter 2 Condition of the Nation’s Streams

Highlight

Nutrients and Eutrophication in Streams

Eutrophication is a condition characterized by excessive plant growth that results from high 

levels of nutrients in a waterbody. Although eutrophication is a natural process, human activities 

can accelerate this condition by increasing the rate at which nutrients and organic substances enter 

waters from their surrounding watersheds. Agricultural runoff, urban runoff, leaking septic systems, 

sewage discharges, eroded streambanks, and similar sources can increase the fl ow of nutrients and 

organic substances into streams, and subsequently, into downstream lakes and estuaries. These 

substances can overstimulate the growth of algae and aquatic plants, creating eutrophic conditions 

that interfere with recreation and the health and diversity of insects, fi sh, and other aquatic 

organisms. 

Nutrient enrichment due to human activities has long been recognized as one of the leading 

problems facing our nation’s lakes, reservoirs, and estuaries. It has also been more recently 

recognized as a contributing factor to stream degradation. In broadest terms, nutrient overenrichment of streams is a problem because of the negative impacts on aquatic life (the focus of 

the WSA); adverse health effects on humans and domestic animals; aesthetic and recreational use 

impairment; and excessive nutrient input into downstream waterbodies, such as lakes.

Excess nutrients in streams can lead to excessive growth of phytoplankton (free-fl oating 

algae) in slow-moving rivers, periphyton (algae attached to the substrate) in shallow streams, and 

macrophytes (aquatic plants large enough to be visible to the naked eye) in all waters. Unsightly 

fi lamentous algae can impair the aesthetic enjoyment of streams. In more extreme situations, 

excessive growth of aquatic plants can slow water fl ow in fl at streams and canals, interfere with 

swimming, snag fi shing lures, and clog the screens on water intakes of water treatment plants and 

industries.

Nutrient enrichment in streams has also been demonstrated to affect animal communities in 

these waterbodies (see the References section at the end of this report for examples of published 

studies). For example, declines in invertebrate community structure have been correlated directly 

with increases in phosphorus concentration. High concentrations of nitrogen in the form of 

ammonia (NH3

) are known to be toxic to aquatic animals. Excessive levels of algae have also been 

shown to be damaging to invertebrates. Finally, fi sh and invertebrates will experience growth 

problems and can even die if either oxygen is depleted or pH increases are severe; both of these 

conditions are symptomatic of eutrophication. 

As a system becomes more enriched by nutrients, different species of algae may spread and 

species composition can shift; however, unless such species shifts cause clearly demonstrable 

symptoms of poor water-quality—such as fi sh kills, toxic algae, or very long streamers of 

fi lamentous algae—the general public is unlikely to be aware of a potential ecological concern.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

35

Phosphorus infl ux leads to increased algal 

growth, which reduces dissolved oxygen levels and 

water clarity within the stream. (See Highlight: 

Nutrients and Eutrophication in Streams for 

more information about the impacts of excess 

phosphorus and nitrogen.) Phosphorus is a 

common component of fertilizers, and high 

phosphorus concentrations in streams may be 

associated with poor agricultural practices, urban 

runoff, or point-source discharges (e.g., effl uents 

from sewage treatment plants).

Findings for Total Phosphorus 

Approximately 31% of the nation’s stream 

length (207,355 miles) has high concentrations 

of phosphorus, 16% (108,039 miles) has medium 

concentrations, and 49% (327,473 miles) has 

low concentrations (Figure 15). Of the three 

major regions, the Eastern Highlands has the 

greatest proportion of stream length with high 

concentrations of phosphorus (43%, or 117,730 

miles), followed by the Plains and Lowlands 

(25%, or 60,324 miles) and the West (19%, or 

28,174 miles) regions. 

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60 70

Percentage of Stream Miles

Stream Length (mi)

89,246

34,693

28,174

312

Total: 152,425

327,473

108,039

207,355

28,184

Total: 671,051

90,647

41,731

117,730

26,254

Total: 276,362

148,508

32,221

60,324

1,211

Total: 242,264

22.8%

18.5%

58.5%

32.8%

15.1%

42.6%

9.5%

L

M

H

N/A

13.3%

24.9%

0.5%

48.8%

16.1%

30.9%

4.2%

L 61.5%

M

H

N/A

L

M

H

N/A

L

M

H

N/A

0.2%

Low Medium High Not Assessed

Figure 15. Total phosphorus concentrations in U.S. streams (U.S. EPA/WSA). Percent of stream length 

with low, medium, and high concentrations of phosphorus based on regionally relevant thresholds derived 

from the least-disturbed regional reference sites. Low concentrations are most similar to reference condition; 

medium concentrations are greater than the 75th percentile of reference condition; and high concentrations are 

greater than the 95th percentile of reference condition.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

36

Chapter 2 Condition of the Nation’s Streams

Total Nitrogen Concentrations

Nitrogen, another nutrient, is particularly 

important as a contributor to coastal and 

estuarine algal blooms. Nitrogen is the primary 

nutrient limiting algal growth in some regions 

of the United States, particularly in granitic or 

basaltic geology found in parts of the Northeast 

and the Pacifi c Northwest. Increased nitrogen 

inputs to a stream can stimulate growth of excess 

algae, such as periphyton, which results in low 

dissolved oxygen levels, a depletion of sunlight 

available to the streambed, and degraded habitat 

conditions for benthic macroinvertebrates and 

other aquatic life (see Highlight: Nutrients and 

Eutrophication in Streams). Common sources of 

excess nitrogen include fertilizers, wastewater, 

animal wastes, and atmospheric deposition.

Findings for Total Nitrogen

A signifi cant portion of the nation’s stream 

length (32%, or 213,394 miles) has high 

concentrations of nitrogen compared to leastdisturbed reference conditions, 21% (138,908 

miles) has medium concentrations, and 43% 

(290,565 miles) has relatively low concentrations 

(Figure 16). As with phosphorus, the Eastern 

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60

Percentage of Stream Miles

Stream Length (mi)

78,346

42,527

31,247

305

Total: 152,425

290,565

138,908

213,394

28,184

Total: 671,051

87,297

45,410

117,284

26,371

Total: 276,362

125,785

49,454

65,715

1,310

Total: 242,264

43.3%

20.7%

31.8%

4.2%

L

M

H

N/A

31.6%

16.4%

42.4%

9.6%

L

M

H

N/A

20.4%

27.1%

0.6%

L 51.9%

M

H

N/A

27.9%

20.5%

L 51.4%

M

H

N/A 0.2%

Low Medium High Not Assessed

Figure 16. Total nitrogen concentrations in U.S. streams (U.S. EPA/WSA). Percent of stream length 

with low, medium, and high concentrations of nitrogen based on regionally relevant thresholds derived from the 

least-disturbed regional reference sites. Low concentrations are most similar to reference condition; medium 

concentrations are greater than the 75th percentile of reference condition; and high concentrations are greater 

than the 95th percentile of reference condition.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

37

Highlands region has the greatest proportion 

of stream length with high concentrations of 

nitrogen (42%, or 117,284 miles), followed by 

the Plains and Lowlands (27%, or 65,715 miles) 

and the West (21%, or 31,247 miles). 

Salinity

Excessive salinity occurs in areas with high 

evaporative losses of water and can be exacerbated 

by repeated use of water for irrigation or by 

water withdrawals. Both electrical conductivity 

and total dissolved solids (TDS) can be used as 

measures of salinity; however, conductivity was 

used for the WSA.

Findings for Salinity

Roughly 3% of the nation’s stream length 

(19,889 miles) has high levels of salinity, 10% 

(69,585 miles) has medium levels, and 83% 

(553,530 miles) has low levels compared to levels 

found in least-disturbed reference sites for the 

nine WSA ecoregions (Figure 17). The Plains 

and Lowlands region has the greatest proportion 

of stream length with high levels of salinity (5%, 

or 12,113 miles), followed by the West (3%, 

or 4,009 miles) and Eastern Highlands (1%, or 

3,593 miles).

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60 70 80 90 100

Percentage of Stream Miles

Stream Length (mi)

137,369

10,735

4,009

312

Total: 152,425

82.5% 553,530

69,585

2.9% 19,889

4.2% 28,047

Total: 671,051

78.8% 217,773

10.4% 28,742

3,593 1.3%

9.5% 26,254

Total: 276,362

198,414 81.9%

30,525 12.6%

12,113 5.0%

1,212 0.5%

Total: 242,264

7.1%

2.6%

10.4%

90.1%

L

M

H

N/A

L

M

H

N/A

L

M

H

N/A

L

M

H

N/A 0.2%

Low Medium High Not Assessed

Figure 17. Salinity conditions in U.S. streams (U.S. EPA/WSA). This indicator is based on electrical 

conductivity measured in water samples. Thresholds are based on conditions at least-disturbed regional 

reference sites.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

38

Chapter 2 Condition of the Nation’s Streams

Acidifi cation

Streams and rivers can become acidic through 

the effects of acid deposition (e.g., acid rain) or 

acid mine drainage, particularly from coal 

mining. Previous studies have shown that these 

issues, while of concern, tend to be focused in a 

few geographic regions of the country. Streams 

and rivers can also be acidic because of natural 

sources, such as high levels of dissolved organic 

compounds. The WSA identifi es the extent of 

systems that are not acidic, naturally acidic (i.e., 

similar to reference), and acidic because of 

anthropogenic disturbance. This last category 

includes streams that are acidic because of 

deposition (either chronic or episodic) or because 

of mine drainage.

Acid rain forms when smokestack and 

automobile emissions (particularly sulfur dioxide 

and nitrogen oxides) combine with moisture in 

the air to form dilute solutions of sulfuric and 

nitric acid. Acid deposition can also occur in dry 

form, such as the particles that make up soot. 

When wet and dry deposition fall on sensitive 

watersheds, they can have deleterious effects on 

soils, vegetation, and streams and rivers. 

In assessing acid rain’s effects on fl owing 

waters, the WSA relied on a measure of the 

water’s ability to buffer inputs of acids, called 

acid-neutralizing capacity (ANC). When ANC 

values fall below zero, the water is considered 

acidic and can be either directly or indirectly 

toxic to biota (i.e., by mobilizing toxic metals, 

such as aluminum). When ANC is between 0 

and 25 milliequilivents, the water is considered 

sensitive to episodic acidifi cation during rainfall 

events. These threshold values were determined 

based on values derived from the National Acid 

Precipitation Assessment Program (NAPAP).

Acid mine drainage forms when water moves 

through mines and mine tailings, combining 

with sulfur released from certain minerals to form 

strong solutions of sulfuric acid and mobilize 

many toxic metals. As in the case of acid rain, 

the acidity of waters in mining areas can be 

assessed by using ANC values. Mine drainage 

also produces extremely high concentrations 

of sulfate—much higher than those found in 

acid rain. Although sulfate is not directly toxic 

to biota, it serves as an indicator of mining’s 

infl uence on streams and rivers. When ANC 

values and sulfate concentrations are low, acidity 

can be attributed to acid rain. When ANC values 

are low and sulfate concentrations are high, 

acidity can be attributed to acid mine drainage. 

Mine drainage itself, even if not acidic, can harm 

aquatic life; however, the WSA does not include 

an assessment of the extent of mine drainage that 

is not acidic.

Acidic mine drainage forms when water moves 

through mines and mine tailings (Photo courtesy 

of Ben Fertig, IAN Image Library). 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

39

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60 70 80 90 100

Percentage of Stream Miles

Stream Length (mi)

151,358

0

762

305

Total: 152,425

625,420

3,355

2.2% 14,763

4.1% 27,513

Total: 671,051

240,711

0 0

9,396 3.4%

9.5% 26,255

Total: 276,362

233,542

3,392 1.4%

4,603 1.9%

727 0.3%

Total: 242,264

0

0.5%

0.5%

G

F

P

N/A

G

F

P

N/A

G

F

P

N/A

G

F

P

N/A

93.2%

87.1%

96.4%

99.3%

0.2%

Good (not acidic) Fair (naturally acidic) Poor (anthropogenically acidic) Not Assessed

Figure 18. Acidifi cation in U.S. streams (U.S. EPA/WSA). Streams are considered acidic when ANC values 

fall below zero. Streams are considered sensitive to acidifi cation during rainfall events when ANC values are 

between 0 and 25 milliequilivents. Both ranges were scored as anthropogenically acidic in poor condition. Acidic 

streams with high concentrations of sulfate are associated with acid mine drainage, whereas low concentrations 

of sulfate indicate acidifi cation due to acid rain.

Findings for Acidifi cation

Figure 18 shows that about 2% of the nation’s 

stream length (14,763 miles) is impacted by 

acidifi cation from anthropogenic sources. These 

sources include acid deposition (0.7%), acid 

mine drainage (0.4%), and episodic acidicity 

due to high-runoff events (1%). Although these 

percentages appear relatively small, they refl ect a 

signifi cant impact in certain parts of the United 

States, particularly in the Eastern Highlands 

region, where 3% of the stream length (9,396 

miles) is impacted by acidifi cation.

Physical Habitat Stressors

A number of human activities can potentially 

impact the physical habitat of streams upon which 

the biota rely. Soil erosion from road construction, 

poor agricultural practices, and other disturbances 

can result in increases in the amount of fi ne 

sediment on the stream bottom; these sediments 

can negatively impact macroinvertebrates and fi sh. 

Physical alterations to vegetation along stream 

banks, alterations to the physical characteristics 

within the stream itself, and changes in the fl ow of 

water all have the potential to impact stream biota. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

40

Chapter 2 Condition of the Nation’s Streams

Although many aspects of stream and river 

habitats can become stressful to aquatic organisms 

when these aspects are modifi ed, the WSA focuses 

on four specifi c stressors as habitat indicators: 

streambed sediments, in-stream fi sh habitat, 

riparian vegetation, and riparian disturbance.

Streambed Sediments

The supply of water and sediments from 

drainage areas affects the shape of river channels 

and the size of streambed particles in streams 

and rivers. One measure of the interplay between 

sediment supply and transport is relative bed 

stability (RBS). The measure of RBS used in 

the WSA is a ratio that compares measures of 

particle size of observed sediments to the size of 

sediments that each stream can move or scour 

during its fl ood stage (based on measures of the 

size, slope, and other physical characteristics of 

the stream channel). The expected RBS ratio 

differs naturally among regions, depending 

upon landscape characteristics, such as geology, 

topography, hydrology, natural vegetation, and 

natural disturbance history. 

Values of the RBS ratio can be either 

substantially lower (e.g., fi ner, more unstable 

streambeds) or higher (e.g., coarser, more stable 

streambeds) than those expected, based on 

the range found at least-disturbed reference 

sites. Both high and low values are considered 

to be indicators of ecological stress. Excess 

fi ne sediments in a stream bed can destabilize 

streams when the supply of sediments from the 

landscape exceeds the ability of the stream to 

move them downstream. This imbalance results 

from a number of human uses of the landscape, 

including agriculture, road building, construction, 

and grazing. Streams with signifi cantly more 

stable streambeds than reference condition (e.g., 

evidence of hardening and scouring, streams that 

have been lined with concrete) were not included 

in the assessment of this indicator. These stream 

conditions occurred so rarely in the survey that 

it was not necessary to separate them from the 

overall population. The WSA focuses on increases 

in streambed sediment levels, represented by 

lower-than-expected streambed stability as the 

indicator of concern.

Lower-than-expected streambed stability may 

result either from high inputs of fi ne sediments 

(e.g., erosion) or increases in fl ood magnitude 

or frequency (e.g., hydrologic alteration). When 

low RBS results from inputs of fi ne sediment, the 

sediment can fi ll in the habitat spaces between 

stream cobbles and boulders. The instability 

(low RBS) resulting from hydrologic alteration 

can be a precursor to channel incision and gully 

formation. 

WSA researchers collected data on indicators 

of biological condition and aquatic indicators of 

stress at 1,392 wadeable stream locations in the 

conterminous United States (Photo courtesy of 

Tetra Tech, Inc.). 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

41

Findings for Streambed Sediments

Approximately 25% of the nation’s stream 

length (167,092 miles) has streambed sediment 

characteristics in poor condition compared 

to regional reference condition (Figure 19). 

Streambed sediment characteristics are rated fair 

in 20% of the nation’s stream length (132,197 

miles) and good in 50% of stream length 

(336,196 miles) compared to reference condition. 

The two regions with the greatest percentage of 

stream length in poor condition for streambed 

sediment characteristics are the Eastern Highlands 

(28%, or 77,381 miles) and the Plains and 

Lowlands (26%, or 63,958 miles), whereas the 

West has the lowest percentage of stream length 

(17%, or 26,522 miles) in poor condition for this 

indicator. 

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

Percentage of Stream Miles

Stream Length (mi)

91,912

31,705

26,522

2,286

Total: 152,425

336,196

132,197

167,092

35,566

Total: 671,051

100,043

70,196

77,381

28,742

Total: 276,362

143,178

30,283

63,958

4,845

Total: 242,264

0 10 20 30 40 50 60 70

G 50.1%

F 19.7%

P 24.9%

N/A 5.3%

G 36.2%

F 25.4%

P 28.0%

N/A 10.4%

G

F 12.5%

P 26.4%

N/A

59.1%

2.0%

G

F 20.8%

P 17.4%

N/A

60.3%

1.5%

Good Fair Poor Not Assessed

Figure 19. Streambed sediments in U.S. streams (U.S. EPA/WSA). This indicator measures the percentage 

of streambeds impacted by increased sedimentation, which indicates alteration from reference condition as 

defi ned by least-disturbed reference sites in each of the nine WSA ecoregions.

In-stream Fish Habitat

The most diverse fi sh and macroinvertebrate 

assemblages are found in streams and rivers that 

have complex forms of habitat, such as boulders, 

undercut banks, tree roots, and large wood within 

the stream banks. Human use of streams and 

riparian areas often results in the simplifi cation of 

this habitat, with potential effects on biological 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

42

Chapter 2 Condition of the Nation’s Streams

integrity. The WSA used a habitat complexity 

measure that sums the amount of in-stream fi sh 

concealment features and habitat consisting of 

undercut banks, boulders, large pieces of wood, 

brush, and cover from overhanging vegetation 

within a stream and its banks.

Findings for In-stream Fish Habitat

Twenty percent of the nation’s stream length 

(130,928 miles) is in poor condition for instream fi sh habitat, 25% (166,851 miles) is in fair 

condition, and 52% (345,766 miles) is in good 

condition compared to least-disturbed reference 

condition (Figure 20). In the three major regions, 

the highest proportion of stream length in poor 

condition for in-stream habitat is in the Plains 

and Lowlands (37%, or 89,638 miles), whereas 

only 12% of stream length (18,748 miles) in the 

West and 8% of stream length (22,797 miles) in 

the Eastern Highlands region is rated poor for this 

indicator.

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

Percentage of Stream Miles

Stream Length (mi)

101,210

32,162

18,748

305

Total: 152,425

345,766

166,851

130,928

27,506

Total: 671,051

154,284

72,910

22,797

26,371

Total: 276,362

91,333

60,566

89,638

727

Total: 242,264

0 10 20 30 40 50 60 70

G 51.5%

F 24.9%

P 19.5%

N/A 4.1%

G 55.8%

F 26.4%

P 8.3%

N/A 9.5%

G 37.7%

F 25.0%

P 37.0%

N/A 0.3%

G

F 21.1%

P 12.3%

N/A

66.4%

0.2%

Good Fair Poor Not Assessed

Figure 20. In-stream fi sh habitat in U.S. streams (U.S. EPA/WSA). This indicator sums the amount of 

in-stream habitat that fi eld crews found in streams. Habitat consisted of undercut banks, boulders, large pieces 

of wood, and brush. Thresholds are based on conditions at regional reference sites.

Riparian Vegetative Cover

The presence of complex, multi-layered 

vegetative cover in the corridor along a stream or 

river is a measure of how well the stream network 

is buffered against sources of stress in the 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

43

watershed. Intact riparian areas can help reduce 

nutrient and sediment runoff from the 

surrounding landscape, prevent streambank 

erosion, provide shade to reduce water 

temperature, and provide leaf litter and large 

wood to serve as food and habitat for stream 

organisms. The presence of large, mature canopy 

trees in the riparian corridor indicates riparian 

longevity; the presence of smaller woody 

vegetation typically indicates that riparian 

vegetation is reproducing and suggests the 

potential for future sustainability of the riparian 

corridor. The WSA uses a measure of riparian 

vegetative cover that sums the amount of woody 

cover provided by three layers of riparian 

vegetation: the ground layer, woody shrubs, and 

canopy trees.

Findings for Riparian Vegetative Cover

Nineteen percent of the nation’s stream length 

(129,748 miles) is in poor condition due to 

severely simplifi ed riparian vegetation, 28% of 

stream length (190,034 miles) is in fair condition, 

and almost 48% (319,548 miles) is in good 

condition relative to least-disturbed reference 

condition in each of the nine WSA ecoregions 

(Figure 21). The West (12%, or 18,596 miles) 

and Eastern Highlands (18%, or 48,640 miles) 

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60

Percentage of Stream Miles

Stream Length (mi)

87,035

46,489

18,596

305

Total: 152,425

319,548

190,034

129,748

31,721

Total: 671,051

116,625

84,843

48,640

26,254

Total: 276,362

115,156

59,245

62,881

4,982

Total: 242,264

G

F 30.5%

P 12.2%

N/A

G 47.6%

F 28.3%

P 19.3%

N/A 4.7%

G 42.2%

F 30.7%

P 17.6%

N/A 9.5%

G 47.5%

F 24.5%

P 26.0%

N/A 2.1%

57.1%

0.2%

Good Fair Poor Not Assessed

Figure 21. Riparian vegetative cover in U.S. streams (U.S. EPA/WSA). This indicator sums the amount of 

woody cover provided by three layers of riparian vegetation: the ground layer, woody shrubs, and canopy trees. 

Thresholds are based on conditions at regional reference sites. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

44

Chapter 2 Condition of the Nation’s Streams

regions have similar proportions of stream length 

with riparian vegetation in poor condition, 

though this equates to a greater number of 

stream miles in the Eastern Highlands region, 

where water is more abundant. In the Plains and 

Lowlands region, a larger proportion of stream 

length (26%, or 62,881 miles) has riparian 

vegetation in poor condition. 

Riparian Disturbance

The vulnerability of the stream network to 

potentially harmful human activities increases 

with the proximity of those activities to the 

streams. The WSA uses a direct measure of 

riparian human disturbance that tallies 11 specifi c 

forms of human activities and disturbances 

along the stream reach and their proximity to a 

stream in 22 riparian plots along the stream. For 

example, streams scored medium if one type of 

human infl uence was noted in at least one-third 

of the plots, and streams scored high if one or 

more types of disturbance were observed in the 

stream or on its banks at all of the plots.

Findings for Riparian Disturbance

Twenty-six percent of the nation’s stream 

length (171,118 miles) has high levels of human 

infl uence along the riparian zone that fringes 

stream banks, and 24% of stream length (158,368 

miles) has relatively low levels of disturbance 

(Figure 22). The Eastern Highlands region has 

the greatest proportion of stream length with 

high riparian disturbance (29%, or 79,591 miles), 

followed by the Plains and Lowlands (26%, or 

62,504 miles) and the West (19%, or 29,570 

miles). One of the striking fi ndings of the WSA 

is the widespread distribution of intermediate 

levels of riparian disturbance; 47% of the nation’s 

stream length (314,052 miles) has intermediate 

levels of riparian disturbance when compared to 

reference condition, and similar percentages are 

found in each of the three major regions.

It is worth noting that for the nation 

and the three regions, the amount of stream 

length with good riparian vegetative cover was 

signifi cantly greater than the amount of stream 

length with low levels of human disturbance 

in the riparian zone. This fi nding warrants 

The most diverse fi sh and macroinvertebrate 

assemblages are found in streams and rivers 

that have complex forms of habitat, such as 

boulders, undercut banks, tree roots, and 

large wood within the stream banks (Photo 

courtesy of Michael L. Smith, F WS). 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

45

Figure 22. Riparian disturbance in U.S. streams (U.S. EPA/WSA). This indicator is based on fi eld 

observations of 11 different types of human infl uence (e.g., dams, pavement, pasture) and their proximity to 

a stream in 22 riparian plots along the stream. 

National

(lower 48)

Eastern

Highlands

Plains and

Lowlands

West

0 10 20 30 40 50 60

Percentage of Stream Miles

Stream Length (mi)

52,739

69,811

29,570

305

Total: 152,425

158,368

314,052

171,118

27,513

Total: 671,051

58,703

111,697

79,591

26,371

Total: 276,362

45,546

133,487

62,504

727

Total: 242,264

L 23.6%

M 46.8%

H 25.5%

N/A 4.1%

L 21.3%

M 40.4%

H 28.8%

N/A 9.5%

L 18.8%

M

H 25.8%

N/A 0.3%

55.1%

L 34.6%

M 45.8%

H 19.4%

N/A 0.2%

Low Medium High Not Assessed

additional investigation, but suggests that land 

managers and property owners are protecting and 

maintaining healthy riparian vegetation buffers, 

even along streams where disturbance from roads, 

agriculture, and grazing is widespread. 

Biological Stressors

Although most of the factors identifi ed as 

stressors to streams and rivers are either chemical 

or physical, there are biological factors that also 

create stress in wadeable streams. Biological 

assemblages can be stressed by the presence of 

non-native species that can either prey on, or 

compete with, native species. In many cases, nonnative species have been intentionally introduced 

to a waterbody; for example, brown trout and 

brook trout are common inhabitants of streams in 

the higher elevation areas of the West, where they 

have been stocked as game fi sh.

When non-native species become established in 

either vertebrate or invertebrate assemblages, their 

presence confl icts with the defi nition of biological 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

46

Chapter 2 Condition of the Nation’s Streams

integrity that the CWA is designed to protect 

(i.e., “having a species composition, diversity, and 

functional organization comparable to that of the 

natural habitat of the region”). Therefore, to the 

extent that non-native species compete with and 

potentially exclude native species, they might be 

considered a threat to biological integrity. These 

indicators were not included in the WSA, but 

may be included in future assessments. 

Ranking of Stressors

A prerequisite to making policy and 

management decisions is to understand the 

relative magnitude or importance of potential 

stressors. It is important to consider both the 

prevalence of each stressor (i.e., what is its extent, 

in miles of stream, and how does it compare to 

other stressors) and the severity of each stressor 

(i.e., how much infl uence does it have on 

biological condition, and is its infl uence greater 

or smaller than the infl uence of other stressors). 

The WSA presents separate rankings of the 

extent and the relative severity of stressors to the 

nation’s fl owing waters. Ideally, both of these 

factors (extent and effect) should be combined 

into a single measure of relative importance. 

EPA is pursuing methodologies for combining 

the two rankings and will present them in future 

assessments.

Extent of Stressors

Figure 23 shows the WSA stressors ranked 

according to the proportion of stream length that 

is in poor condition. Results are presented for 

the nation (top panel) and for each major region, 

with the stressors ordered (in all panels) according 

to their relative extent nationwide. 

Little Washita River, OK, in the Plains and Lowlands region (Photo courtesy of Monty 

Porter).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

47

Figure 23 reveals that excess total nitrogen 

is the most pervasive stressor for the nation, 

although it is not the most pervasive in each 

region. Approximately 32% of the nation’s stream 

length (213,394 miles) shows high concentrations 

of nitrogen compared to reference conditions. 

In the Plains and Lowlands region, nitrogen 

is at high concentrations in 27% of stream 

length (65,715 miles), whereas this proportion 

climbs to 42% (117,285 miles) in the Eastern 

Highlands region. Even in the West, where levels 

of disturbance are generally lower than the other 

major regions, excess total nitrogen is found 

in 21% of the stream length (31,247 miles). 

Phosphorus exhibits comparable patterns to 

nitrogen and is the second most-pervasive stressor 

for the nation’s stream length. 

National 

(lower 48) 

Eastern 

Highlands 

Plains and 

Lowlands 

West 

0 10 20 30 40 50 

Percentage of Stream Miles 

Stream Length (mi) 

N 31.8%

P 30.9%

RD 25.5%

SS 24.9%

I-sFH 19.5%

RVC 19.3%

S 2.9%

A

N 42.4%

P 42.6%

RD 28.8%

SS 28.0%

I-sFH 8.3%

RVC 17.6%

S 1.3%

A 3.4%

N

P

RD

SS

I-sFH

RVC

S

A

N 

P 

RD 

SS 

I-sFH 

RVC 

S 

A 

27.1%

24.9%

25.8%

26.4%

37.0%

26.0%

5.0%

20.5%

18.5%

19.4%

17.4%

12.3%

12.2%

2.6%

0.5%

213,394

207,355

171,118

167,092

130,928

129,748

19,889

2.2% 14,763

117,284

117,730

79,591

77,381

22,797

48,640

3,593

9,396

65,715

60,324

62,504

63,958

89,638

62,881

12,113

1.9% 4,603

31,247

28,174

29,570

26,522

18,748

18,596

4,009

762

N = Nitrogen I-sFH = In-stream Fish Habitat 

P = Phosphorus RVC = Riparian Vegetative Cover 

RD = Riparian Disturbance S = Salinity 

SS = Streambed Sediments A = Acidification 

Figure 23. Extent of stressors (i.e., proportion of stream length ranked in poorest category for each stressor) 

(U.S. EPA/WSA).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

48

Chapter 2 Condition of the Nation’s Streams

The least-common stressors for the nation’s 

stream length are salinity and acidifi cation. Only 

3% (19,889 miles) and 2% (14,763 miles), 

respectively, of the nation’s stream length is in 

poor condition for salinity and acidifi cation levels. 

Although these stressors are not present in large 

portions of the nation’s streams, they can have a 

signifi cant impact where they do occur.

The extent of stressors measured in the WSA 

varies across the three major regions. In the Plains 

and Lowlands region, the stressor rated poor for 

the greatest proportion of stream length (37%, or 

89,638 miles) is loss of in-stream fi sh habitat. In 

the Eastern Highlands region, high total nitrogen 

and total phosphorus concentrations were found 

in more than 42% of the stream length (117,285 

and 117,730 miles, respectively). In the West, 

no stressor is found to affect more than 21% of 

stream length (31,247 miles), although nitrogen, 

phosphorus, and riparian disturbance are the 

most widespread stressors in this region as well. 

Relative Risk of Stressors to 

Biological Condition

This report borrows the concept of relative risk 

from the medical fi eld to address the question of 

severity of stressor effects. We have all heard that 

we run a greater risk of developing heart disease if 

we have high cholesterol levels. Often such results 

are presented in terms of a relative-risk ratio (e.g., 

the risk of developing heart disease is 4 times 

higher for a person with a total cholesterol level 

greater than 300 mg than for a person with a total 

cholesterol level of less than 150 mg). 

The relative-risk values for aquatic stressors 

can be interpreted in the same way as the 

cholesterol example. For each of the key stressors, 

Figure 24 depicts how much more likely a stream 

is to have poor biological condition if stream 

length is in poor condition for a stressor or if high 

concentrations of a stressor are present than if the 

stream length is in good condition for a stressor 

or a stressor is found at low concentrations. 

Because different aspects of the macroinvertebrate 

assemblage (i.e., biological condition vs. taxa loss) 

are expected to be affected by different stressors, 

the WSA calculates relative risk separately for 

each of the two biological condition indicators 

(Macroinvertebrate Index and O/E Taxa Loss). 

A relative-risk value of 1 indicates that there 

is no association between the stressor and the 

biological indicator, whereas values greater than 1 

suggest that the stressor poses a greater relative risk 

to biological condition. The WSA also calculates 

confi dence intervals (Figure 24) for each relative 

risk ratio. When the confi dence interval extending 

above and below the ratio does not overlap the 

value of 1, the relative risk estimate is statistically 

signifi cant.

The relative risks shown in Figure 24 provide 

an estimate of the severity of each stressor’s 

effect on the macroinvertebrate community in 

streams. Almost all of the stressors evaluated 

for the WSA were associated with increased 

risk for macroinvertebrates. Evaluating relative 

risk provides insight on which stressors might 

be addressed to improve biological condition. 

Excess nitrogen, phosphorus, and streambed 

sediments stand out as having the most signifi cant 

impacts on biological condition based on both 

the Macroinvertebrate Index and O/E Taxa Loss 

indicators. Findings show that streams with 

relatively high concentrations of nutrients or excess 

streambed sediments are two to four times more 

likely to have poor macroinvertebrate condition. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 2 Condition of the Nation’s Streams

49

National

(lower 48)

Eastern 

Highlands 

Plains and 

Lowlands 

West 

0 10 20 30 40 

Percentage Stream Length in Most Relative Risk Relative Risk

Disturbed Condition

N 31.8%

P 30.9%

RD 25.5%

SS 24.9%

I-SFH 19.5%

RVC 19.3%

S 2.9%

A 

N 

P 

RD 28.8% 

SS 28.0%

I-SFH 8.3%

RVC 17.6%

S 1.3% 

A 

N 

P 

RD 

SS 

I-SFH 

RVC 

S 

A 

N 

P 

RD 

SS 

I-SFH 

RVC 

S 

A 

1.1

2.0

1.2

1.3

1.4

27.1% 1.8

24.9% 2.2

25.8% 1.9

26.4% 2.3

37.0% 1.7

26.0% 1.7

5.0% 1.8

3.2

1.5 

3.6

1.7 

3.1

2.5

N = Nitrogen I-sFH = In-stream Fish Habitat

P = Phosphorus RVC = Riparian Vegetative Cover

1 2 3 4 1 2 3 4 5 

2.1 2.5

2.2 2.5

1.4 1.5 

2.4 2.9

1.4 1.7

1.6 1.8

1.7 1.4

2.2%

42.4% 1.7 2.1 

42.6% 1.7 1.9 

1.1

2.7

1.6

1.8 

2.1 

2.0

2.6

1.2 

2.5

2.0

1.1

0.8

3.6

3.1

2.3 

3.0

2.5 

3.2

Relative Risk to Relative Risk

Macroinvertebrate O/E

Extent of Stressor Condition Taxa Loss

1.9%

20.5%

18.5%

19.4%

17.4%

12.3%

12.2%

2.6%

RD = Riparian Disturbance S = Salinity

SS = Streambed Sediments A = Acidification

4.0

0.5%

3.4%

4.5

Figure 24. Extent of stressors and their relative risk to Macroinvertebrate Condition and O/E 

Taxa Loss (U.S. EPA/WSA). This fi gure shows the association between a stressor and biological condition and 

answers the question, “What is the increased likelihood of poor biological condition when stressor X is rated 

in poor condition?” It is important to note that this fi gure treats each stressor independently and does not 

account for the effects of combinations of stressors.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

50

Chapter 2 Condition of the Nation’s Streams

There are differences in relative risk from 

a geographic perspective. In general, the West 

exhibits a higher relative risk for the majority 

of stressors than the Eastern Highlands and 

the Plains and Lowlands regions. There are 

also differences associated with the different 

indicators of biological condition. The O/E 

Taxa Loss indicator has somewhat higher relative 

risk ratios for most of the stressors than the 

Macroinvertebrate Index. Additional analysis is 

needed to further explore these differences.

In this assessment of relative risk, it is 

impossible to separate completely the effects 

of the individual stressors that often occur 

together. For example, streams with high nitrogen 

concentrations often exhibit high phosphorus 

concentrations, and streams with high riparian 

disturbance often have sediments far in excess of 

expectations; however, the analysis presented in 

Figure 24 treats the stressors as if they operate 

independently. 

Combining Extent and Relative 

Risk

The most comprehensive assessment of the 

ranking of stressors comes from evaluating both 

the extent (Figure 23) and relative risk (Figure 24) 

results. Stressors that pose the greatest overall risk 

to biological integrity will be those that are both 

widespread (i.e., rank high in terms of the extent 

of stream length in poor condition for a stressor 

in Figure 23) and whose effects are potentially 

severe (i.e., exhibit high relative risk ratios in 

Figure 24). The WSA facilitates this combined 

evaluation of stressor importance by including 

side-by-side comparisons of the extent of stressors 

and relative risk to macroinvertebrate condition 

in Figure 24.

An examination of nationwide results suggests 

some common patterns for key stressors and 

the two indicators of biological condition. Total 

nitrogen, total phosphorus, and excess streambed 

sediments are stressors posing the greatest relative 

risk nationally (relative risk greater than 2), and 

they also occur in 25–32% of the nation’s stream 

length. This suggests that management decisions 

aimed at reducing excess sediment, nitrogen, 

and phosphorus loadings to streams could have a 

positive impact on macroinvertebrate biological 

integrity and prevent further taxa loss across the 

country. 

High salinity in the West is strongly associated 

with a poor Macroinvertebrate Index score 

(relative risk = 2.5) and O/E Taxa Loss score 

(relative risk > 3.1 or = 3.2); however, the rarity of 

this occurrence (salinity affects only 3% of stream 

length in the West region) suggests that excess 

salinity is a local issue requiring a locally targeted 

management approach rather than a national or 

regional effort.

Relative risks for all stressors in the West region 

are consistently larger than for the nation overall 

or for the other two regions, yet the extent of 

streams in poor condition for these stressors is 

consistently lower in the West. This suggests that 

although the stressors are not widespread in the 

West, the region’s streams are particularly sensitive 

to a variety of disturbances. 
51

Chapter 3

tment of Natural Resources tesy of the Georgia Depar Photo cour

Wadeable Streams Assessment 

Ecoregion Results
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

 52

Wadeable Streams

Assessment Ecoregion 

Results

The WSA is designed to report on three 

geographic scales: national, regional, and 

ecoregional. Chapter 2 presented the nationaland regional-scale results, and this chapter will 

focus on the results for the nine WSA ecoregions. 

Ecoregions are areas that contain similar 

environmental characteristics, such as climate, 

vegetation, soil type, and geology. EPA has 

defi ned ecoregions at various scales, ranging from 

coarse (Level I) ecoregions at the continental scale 

to fi ne (Levels III and IV) ecoregions that divide 

states into smaller ecosystem units. Ecoregions are 

designed to be used in environmental assessments, 

for setting water quality and biological criteria, 

and to set management goals for non-point source 

pollution. 

The nine WSA ecoregions are aggregations of 

the Level III ecoregions delineated by EPA for 

the conterminous United States. This chapter 

provides background information on physical 

setting, biological setting, and human infl uence 

for each of the WSA ecoregions and describes 

WSA results for the wadeable stream length 

throughout each ecoregion. The WSA results 

may not be extrapolated to an individual state or 

stream within the ecoregion because the study 

design was not intended to characterize stream 

conditions at these fi ner scales. Note that a 

number of states implement randomized designs 

at the state scale to characterize water quality 

throughout their state, but these characterizations 

are not described in this WSA report. 

The nine ecoregions encompass a variety of 

habitats and land uses, and the least-disturbed 

reference sites used to set benchmarks for good, fair, 

and poor condition refl ect that variability. For some 

ecoregions, the variability among reference sites 

is very small, while it is larger in others. During a 

series of WSA workshops held around the country, 

professional biologists examined the variability of 

reference sites and implications to the benchmarks 

used to characterize an ecoregion and to compare 

stream condition across ecoregions. These 

benchmarks or thresholds were adjusted for those 

ecoregions where there was a disturbance signal 

associated with the variability among reference 

sites. Additional details on the development of 

benchmarks or thresholds for each of the indicators 

can be found in the data analysis method available 

in Chapter 1 and on the EPA Web site at http://

www.epa.gov/owow/streamsurvey.

Manistee River, MI, in the Upper Midwest 

ecoregion (Photo courtesy of the Great Lakes 

Environmental Center).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

53

Figure 25. Ecoregions surveyed for the WSA (U.S. EPA/WSA). 

WSA Ecological Regions*

Northern Appalachians Southern Plains

Southern Appalachians Northern Plains

Coastal Plains Western Mountains

Upper Midwest Xeric

Temporate Plains *based on Omernik Level III ecoregions

• Northern Appalachians

• Southern Appalachians

• Coastal Plains 

• Upper Midwest

• Temperate Plains

• Southern Plains

• Northern Plains

• Western Mountains

• Xeric. 

This report includes brief descriptions of the 

WSA ecoregions. It should be noted that there 

are many specifi c and unique features within each 

ecoregion that are not fully captured in these brief 

descriptions (see the References section at the end 

of this report for more information). The nine 

ecoregions displayed in Figure 25 and defi ned in 

this text are the following:
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

54

Northern Appalachians 

Ecoregion

Physical Setting

The Northern Appalachians ecoregion covers 

all of the New England states, most of New 

York, the northern half of Pennsylvania, and 

northeastern Ohio. This ecoregion encompasses 

New York’s Adirondack and Catskill mountains 

and Pennsylvania’s mid-northern tier, including 

the Allegheny National Forest. Major river 

systems for the Northern Appalachians ecoregion 

are the St. Lawrence, Allegheny, Penobscot, 

Connecticut, and Hudson rivers, and major 

waterbodies include Lake Ontario, Lake Erie, 

New York’s Finger Lakes, and Lake Champlain. 

The total stream length represented in the WSA 

for the Northern Appalachians ecoregion is 

97,913 wadeable stream miles.

The topography of this ecoregion is generally 

hilly, with some intermixed plains and old 

mountain ranges. River channels in the glaciated 

uplands of the northern parts of this ecoregion 

have steep profi les and rocky beds, and fl ow 

over glacial sediments. The climate is cold to 

temperate, with mean annual temperatures 

ranging from 39 to 48 °F. Annual precipitation 

totals range from 35 to 60 inches. The land area 

of Northern Appalachians ecoregion comprises 

some 139,424 mi2

 (4.6% of the United States), 

with about 4,722 mi2

 (3.4%) of land under 

federal ownership. Based on satellite images from 

the 1992 National Land Cover Dataset (NLCD), 

the distribution of land cover in this ecoregion is 

69% forested and 17% planted/cultivated, with 

the remaining 14% of the ecoregion comprised of 

other types of land cover.

Biological Setting

Contemporary fi sh stocks are lower than at the 

time of European contact, but the coastal rivers of 

the Northern Appalachians ecoregion still have a 

wide variety of anadromous fi sh, including shad, 

alewife, salmon, and sturgeon.

Human Infl uence

Early European settlers in 17th-century New 

England removed beaver dams, allowing fl oods 

to pass more quickly, thereby fl ushing sediment 

and decreasing the diversity and availability of 

riparian habitat. Forests were cleared to introduce 

crops and pasture for grazing animals, and these 

efforts caused the erosion of sediments, increased 

nutrients, and reduced riparian habitat. Roughly 

96% of the original virgin forests of the eastern 

and central states were gone by the 1920s. 

Cedar Stream, NH, in the Northern Appalachians 

ecoregion (Photo courtesy of Colin Hill, Tetra Tech, Inc.).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

55

Smaller tributaries in this ecoregion were 

often disrupted through splash damming — a 

19th century practice of creating dam ponds 

for collecting timber and then exploding the 

dams to move timber downstream with the 

resulting torrent of fl ood waters. These waters 

carried fl ushed sediment and wood downstream, 

and these materials scoured many channels to 

bedrock. Streams that were not splash dammed 

currently have tens to hundreds of times more 

naturally occurring woody debris and deeper 

pools. During the 18th and early 19th centuries, 

streams with once-abundant runs of anadromous 

fi sh declined due to stream sedimentation, 

clogging from sawmill discharges, and the effects 

of dams. Increased human and animal waste 

from agricultural communities changed stream 

nutrient chemistry. When agriculture moved west 

and much of the ecoregion’s eastern farmland 

converted back into woodlands, sediment yields 

declined in some areas. 

Today, major manufacturing, chemical, 

steel, and power production (e.g., coal, nuclear, 

oil) occur in the large metropolitan areas 

found around New York City and the states of 

Connecticut and Massachusetts. Many toxic 

substances, including petroleum products, 

organochlorines, polychlorinated biphenyls 

(PCBs), and heavy metals, along with increased 

nutrients such as nitrates and phosphates, are 

the legacy of industrial development. There are 

currently 215 active, 6 proposed, and 45 former 

EPA Superfund National Priority List sites in the 

Northern Appalachian ecoregion.

It is also common for treated wastewater 

effl uent to account for much of the stream fl ow 

downstream from major urban areas in this 

ecoregion. Treated wastewater can be a major 

source of nitrate, ammonia, phosphorus, heavy 

metals, volatile organic chemicals (VOCs), PCBs, 

and other toxic compounds. 

This ecoregion supports forestry; mining; 

fi shing; wood processing of pulp, paper, and 

board; tourism; and agricultural activities, such as 

dairy cattle farming, potato production, poultry 

farming, and timber harvesting. 

The approximate population within the 

Northern Appalachians ecoregion is 40,550,000, 

representing approximately 14% of the total 

population of the United States.

Summary of WSA Findings

A total of 85 WSA sites were sampled during 

the summer of 2004 to characterize the condition 

of wadeable streams in the Northern Appalachians 

ecoregion. An overview of the WSA survey results 

for this ecoregion is shown in Figure 26. These 

results may not be extrapolated to accurately 

assess the ecological condition of an individual 

state or stream within the ecoregion because the 

study design was not intended to characterize 

stream conditions at these fi ner scales.

It should be noted that about 27% of wadeable 

stream length in the Northern Appalachians 

ecoregion was not assessed because small, 

1st-order streams in New England were not 

included in the sample frame. These streams 

were excluded from the WSA due to a decision 

to match an earlier New England random design. 

The numbers cited below apply to the 73% of 

wadeable stream length that was assessed in the 

Northern Appalachians ecoregion. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

56

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Northern Appalachians 

ecoregion said that many least-disturbed reference 

sites in this ecoregion are nearly undisturbed 

streams, with sparse human population in the 

immediate watershed; therefore, the reference 

condition for the ecoregion is of very high quality. 

Biological Condition

• The fi ndings of the Macroinvertebrate Index 

show that 45% of stream length in the 

Northern Appalachians ecoregion is in poor 

condition, 15% is in intermediate or fair 

condition, and 13% is in good condition 

when compared to least-disturbed reference 

condition. As noted above, 1st-order streams, 

which are generally considered to be of high 

quality in this ecoregion, were not included in 

the WSA. 

• The O/E Taxa Loss results show that 50% of 

stream length in the Northern Appalachians 

ecoregion has lost 10% or more of the 

macroinvertebrate taxa expected to occur, and 

19% has lost more than 50% of taxa. These 

results indicate that 23% of stream length has 

retained 90% of the groups or classes of 

organisms expected to occur based on leastdisturbed reference condition.

Indicators of Stress

Leading indicators of stress in the Northern 

Appalachians ecoregion include total phosphorus, 

total nitrogen, streambed sediments, and riparian 

vegetative cover.

Figure 26. WSA survey results for the Northern Appalachians ecoregion (U.S. EPA/WSA). Bars show 

the percentage of stream length within a condition class for a given indicator. Lines with brackets represent 

the width of the 95% confi dence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

0 20 40 60 80 0 20 40 60 80 100

Phosphorus Streambed Sediments

Nitrogen In-stream Fish Habitat 

0 20 40 60 80

Northern Appalachians Ecoregion

97,913 miles

Macroinvertebrate Index

O/E Taxa Loss

12% 28%

16% 14%

45% 29%

27% 29%

18% 44%

10% 13%

45% 16%

27% 27%

Riparian Disturbance Riparian Vegetative Cover

13% 19% 20%

15% 34% 27%

45% 20% 26%

27% 27% 27%

Salinity Acidification

64% 70%

8% 0%

1% 3% 19% 17% 14% 23% 27%

27% 27%

100 100

Percentage Stream Length Percentage Stream Length

Good

Fair

Poor

Not Assessed

Low

Medium

High

Not Assessed

Percentage Stream Length

> 50% Taxa Loss 20–50% Taxa Loss

10–20% Taxa Loss < 10% Taxa Loss

Not Assessed

Good Fair Poor Not Assessed

For O/E Taxa Loss:

For Macroinvertebrate Index:
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

57

• Approximately 45% of stream length in the 

Northern Appalachians ecoregion has high 

phosphorus concentrations, 16% has medium 

phosphorus concentrations, and 12% has low 

phosphorus concentrations based on leastdisturbed reference condition.

• Similarly, approximately 45% of the 

ecoregion’s stream length has high nitrogen 

concentrations, 10% has medium nitrogen 

concentrations, and 18% has low nitrogen 

concentrations based on least-disturbed 

reference condition. 

• Riparian disturbance, or evidence of human 

infl uence in the riparian zone, is at high levels 

in 20% of stream length, at medium levels 

in 34% of stream length, and at low levels in 

19% of stream length.

• Salinity is found at high levels in 1% of stream 

length, at medium levels in 8% of stream 

length, and at low levels in 64% of stream 

length.

• Streambed sediments are rated poor in 29% of 

stream length in the Northern Appalachians 

ecoregion, fair in 14%, and good in 28%. 

• In-stream fi sh habitat is in poor condition in 

16% of stream length, fair in 13% of stream 

length, and good in 44%. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 26% of 

stream length, fair condition for 27% of stream 

length, and good condition for 20% of stream 

length. 

• Acidifi cation, which is primarily associated with 

acid rain in this ecoregion, is rated poor in 3% 

of stream length. 

Stream channels in the glaciated uplands of the Northern Appalachians 

are characterized by steep profi les and rocky beds (Photo courtesy of 

Lauren Holbrook, IAN Image Library).
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

58

Southern Appalachians 

Ecoregion

Physical Setting

The Southern Appalachians ecoregion stretches 

over 10 states, from northeastern Alabama to 

central Pennsylvania, and includes the interior 

highlands of the Ozark Plateau and the Ouachita 

Mountains in Arkansas, Missouri, and Oklahoma.

The land area of the Southern Appalachians 

ecoregion covers about 321,900 mi2

 (10.7% 

of the United States), with about 42,210 mi2

(13.1%) of land under federal ownership. Many 

significant public lands, such as the Great Smoky 

Mountains National Park, the George Washington 

and Monongahela national forests, and the 

Shenandoah National Park, reside within this 

ecoregion. The topography is mostly hills and low 

mountains, with some wide valleys and irregular 

plains. Piedmont areas are included within the 

Southern Appalachians ecoregion.

Rivers in this ecoregion flow mostly over 

bedrock and other resistant rock types, with steep 

channels and short meander lengths. Major rivers 

such as the Susquehanna, James, and Potomac, 

along with feeders into the Ohio and Mississippi 

river systems, such as the Greenbrier River in 

West Virginia, originate in this ecoregion. The 

total stream length represented in the WSA for 

the Southern Appalachians ecoregion is 178,449 

wadeable stream miles.

This ecoregion’s climate is considered 

temperate wet, and annual precipitation 

totals average 40 to 80 inches. Mean annual 

temperature ranges from 55 to 65 °F. Based 

on satellite images in the 1992 NLCD, the 

distribution of land cover in this ecoregion is 68% 

forested and 25% planted/cultivated, with the 

remaining 7% in other types of land cover.

Biological Setting

The Southern Appalachians ecoregion has 

some of the greatest aquatic animal diversity of 

any area in North America, especially for species 

Young Womans Creek, 

PA, in the Southern 

Appalachians 

ecoregion (Photo 

courtesy of the Great 

Lakes Environmental 

Center). 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

59

of amphibians, fishes, mollusks, aquatic insects, 

and crayfishes. Salamanders, plants, and fungi 

reach their highest North American diversity in 

the Southern Appalachians ecoregion; however, 

some 18% of animal and plant species in the 

ecoregion are threatened or endangered. 

Some areas in the Southern Appalachians 

ecoregion are among the least-impacted presettlement vegetative cover in the United States, 

such as the spruce-fir forests in the southern part 

of the ecoregion. The Great Smoky Mountains 

National Park and other national forests continue 

to protect exceptional stands of old-growth forest 

riparian ecosystems.

Human Influence

The effects of habitat fragmentation, urbanization, agriculture, channelization, diversion, and 

impoundments on river systems have altered a 

large amount of stream length in the Southern 

Appalachians ecoregion. Placer mining, which 

disrupts streambeds and increases a stream’s 

ability to transport fine sediments that influence 

habitat and water quality downstream, began in 

the Appalachians in the 1820s. In addition, some 

800 mi2

 were surface mined in the Appalachian 

Highlands between 1930 and 1971, leading 

to the acidification of streams and reduction 

of aquatic diversity. Placer mining and surface 

mining operations have introduced many toxic 

contaminants to river systems in the Southern 

Appalachians ecoregion, including arsenic, 

antimony, copper, chromium, cadmium, 

nickel, lead, selenium, silver, and zinc. There 

are 224 active, 5 proposed, and 46 deleted EPA 

Superfund National Priority List sites in this 

ecoregion.

Economic activities in the Southern 

Appalachians ecoregion include forestry, 

coal mining, and some local agriculture and 

tourism industries. Petroleum and natural gas 

extraction are prevalent along the coal belt, 

and the ecoregion supports coal, bauxite, zinc, 

copper, and chromium mining activities. Utility 

industries include hydro-power in the Tennessee 

Valley and numerous coal-fired plants throughout 

the ecoregion. Significant agricultural activities 

are alfalfa production in Pennsylvania, with apple 

and cattle production occurring throughout the 

ecoregion. Wood processing and pulp, paper, and 

board production are also prevalent. 

Approximately 50,208,000 people live in the 

Southern Appalachians ecoregion, representing 

approximately 17% of the total population of the 

United States. 

Summary of WSA Findings

A total of 184 random sites were sampled 

during the summer of 2004 to characterize the 

condition of wadeable streams in the Southern 

Appalachians ecoregion. An overview of the WSA 

survey results for the ecoregion is shown in Figure 

27. These results may not be extrapolated to an 

individual state or stream within the ecoregion 

because the study design was not intended to 

characterize stream conditions at these finer scales. 

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Southern Appalachians 

ecoregion said that the least-disturbed reference 

streams in the ecoregion represent varying degrees 

of human influence. Although some reference 

streams are in remote areas, others are intricately 

linked with road systems in narrow floodplains. 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

60

Biological Condition

• The Macroinvertebrate Index shows that 55% 

of stream length in the Southern Appalachians 

ecoregion is in poor condition, 24% is in 

fair or intermediate condition, and 21% is in 

good condition compared to least-disturbed 

reference condition. 

• The O/E Taxa Loss results show that 65% of 

stream length in the Southern Appalachians 

ecoregion has lost 10% or more of the 

macroinvertebrate taxa that are expected to 

occur, and 16% has lost more than 50% of 

taxa. These results also indicate that 30% of 

stream length has retained 90% of the groups 

or classes of organisms expected to occur based 

on least-disturbed reference condition.

Indicators of Stress

Leading indicators of stress in the Southern 

Appalachians ecoregion include total nitrogen, 

total phosphorus, riparian disturbance, and 

streambed sediments. 

• Forty-one percent of stream length in the 

Southern Appalachians ecoregion has high 

phosphorus concentrations, 15% has medium 

phosphorus concentrations, and 44% has low 

phosphorus concentrations based on leastdisturbed reference condition. 

• Nitrogen concentrations in the ecoregion 

are high in 41% of stream length, medium 

in 20% of stream length, and low in 39% 

of stream length based on least-disturbed 

reference condition. 

Figure 27. WSA survey results for the Southern Appalachians ecoregion (U.S. EPA/WSA). Bars 

show the percentage of stream length within a condition class for a given indicator. Lines with brackets 

represent the width of the 95% confidence interval around the percent of stream length. Percents may not 

add up to 100 because of rounding.

Phosphorus Streambed Sediments 

Nitrogen In-stream Fish Habitat 

Southern Appalachians Ecoregion 

178,449 miles 

44% 41%

15% 32%

41% 27%

39% 62%

20% 34%

41% 4%

Macroinvertebrate Index Riparian Disturbance Riparian Vegetative Cover

21% 23% 54%

24% 44% 33%

55% 33% 13%

Salinity Acidification 

O/E Taxa Loss 87% 97%

11% 0% 

16% 36% 13% 30% 5% 2% 3% 

0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

61

Sandy Creek, LA, in the Coastal Plains 

ecoregion (Photo courtesy of the Great Lakes 

Environmental Center).

• Riparian disturbance, or evidence of human 

influence in the riparian zone, is at high levels 

in 33% of stream length, at medium levels 

in 44% of stream length, and at low levels in 

23% of stream length.

• Salinity is found at high levels in only 2% of 

stream length, at medium levels in 11% of 

stream length, and at low levels in 87% of 

stream length.

• Streambed sediments are rated poor in 27% 

of stream length in the Southern Appalachians 

ecoregion, fair in 32%, and good in 41%.

• In-stream fish habitat is in poor condition in 

4% of stream length, fair in 34% of stream 

length, and good in 62%. 

• Vegetative cover in the riparian zone along 

Southern Appalachian stream banks is in poor 

condition in 13% of stream length, fair in 

33% of stream length, and good in 54% of 

stream length. 

• Acidification, which is primarily associated 

with acidic deposition and acid mine drainage 

in this ecoregion, is rated poor in 3% of stream 

length.

Coastal Plains Ecoregion

Physical Setting

The Coastal Plains ecoregion covers the 

Mississippi Delta and Gulf Coast, north along the 

Mississippi River to the Ohio River, all of Florida 

and eastern Texas, and the Atlantic seaboard from 

Florida to New Jersey. The total land area of this 

ecoregion is about 395,000 mi2

 (13.2% of the 

United States), with 25,890 mi2

 (6.6%) of land 

under federal ownership. River systems lying 

within or intersecting the Coastal Plains ecoregion 

are the Mississippi, Suwannee, Savannah, 

Roanoke, Potomac, Delaware, Susquehanna, 

James, Sabine, Brazos, and Guadalupe rivers. 

Rivers in the Coastal Plains meander broadly 

across flat plains created by thousands of years 

of river deposition and form complex wetland 

topographies with levees, backswamps, and oxbow 

lakes. Rivers typically drain densely vegetated 

catchment areas, while well-developed soils and 

less intensive rains and subsurface flows keep 

suspended sediment levels in the rivers relatively 

low. The Mississippi River carries large loads 

of sediments from dry lands in the central and 

western portion of the drainage. The total stream 

length represented in the WSA for the Coastal 

Plains ecoregion is 72,130 wadeable stream miles.
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

62

The Coastal Plains ecoregion contains about 

one-third of all remaining U.S. wetlands, more 

than half of U.S. forested wetlands, and the 

largest aggregate area of U.S. riparian habitat. 

The topography of the area is mostly flat plains, 

barrier islands, numerous wetlands, and about 

50 important estuarine systems that lie along the 

coastal margins. The climate of this ecoregion is 

considered temperate wet to subtropical in the 

south, with average annual temperatures ranging 

from 50 to 80 °F and annual precipitation 

ranging from 30 to 79 inches. Based on satellite 

images in the 1992 NLCD, the distribution of 

land cover in this ecoregion is 39% forested, 30% 

planted/cultivated, and 16% wetlands, with the 

remaining 15% of the ecoregion comprised of 

other types of land cover.

Biological Setting

River habitats in the Coastal Plains ecoregion 

have tremendous species richness and the 

highest number of endemic species of aquatic 

organisms in North America. Abundant fish, 

crayfish, mollusk, aquatic insect, and other 

species include such unique species as paddlefish, 

catostomid suckers, American alligator, and giant 

aquatic salamanders; however, it is estimated 

that some 18% of the aquatic species in this 

ecoregion are threatened or endangered. The 

Coastal Plains ecoregion includes the Florida 

Everglades, which contains temperate and 

tropical plant communities and a rich variety of 

bird and wildlife species; however, because it is a 

unique aquatic ecosystem, the Everglades is not 

represented in the WSA.

Human Influence

Historically, the Coastal Plains ecoregion had 

extensive bottomlands that flooded for several 

months; these areas are now widely channelized 

and confined by levees. Damming, impounding, 

and channelization in almost all major rivers 

have altered the rate and timing of water flow, 

as well as the productivity of riparian habitats. 

Pollution from acid mine drainage, urban runoff, 

air pollution, sedimentation, and recreation, as 

well as the introduction of non-indigenous fishes 

and aquatic plants, have also affected riparian 

habitats and native aquatic fauna. There are 

currently 275 active, 13 proposed, and 77 deleted 

EPA Superfund National Priority List sites in the 

Coastal Plains ecoregion.

The ecoregion’s economy is varied and includes 

many activities. Agriculture in this ecoregion 

includes citrus, peanut, sugar cane, tobacco, 

cattle, poultry, cotton, corn, rice, vegetable, 

and stone fruit production. Industries include 

pulp, paper, board, and board wood processing; 

aluminum production; salt, sulfur, bauxite, 

and phosphate mining; and chemical and 

plastics production. The Coastal Plains contain 

approximately 40% of U.S. petrochemical 

refinery capacity, much of which is located 

offshore in the Gulf of Mexico. 

This ecoregion also includes many large 

coastal cities, which contribute to a population of 

approximately 56,168,000, the largest population 

of all the WSA ecoregions, representing 

approximately 19% of the population of the 

United States. 
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Summary of WSA Findings

A total of 83 random sites were sampled during 

the summer of 2004 to characterize the condition 

of wadeable streams in the Coastal Plains 

ecoregion. An overview of the WSA survey results 

for this ecoregion is shown in Figure 28. These 

results may not be extrapolated to an individual 

state or stream within the ecoregion because the 

study design was not intended to characterize 

stream conditions at these finer scales. 

During a series of WSA workshops 

conducted to evaluate assessment results, 

professional biologists working in the Coastal 

Plains ecoregion said that the high prevalence 

of human population centers, agriculture, 

and industry makes it difficult to find truly 

undisturbed streams in this ecoregion; therefore, 

the ecoregion’s least-disturbed reference sites are 

influenced to some degree by human activities. 

Figure 28. WSA survey results for the Coastal Plains ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent 

the width of the 95% confidence interval around the percent of stream length. Percents may not add up to 

100 because of rounding.

Phosphorus Streambed Sediments 

58% 64%

13% 11%

29% 22%

Nitrogen In-stream Fish Habitat 

Coastal Plains Ecoregion 72% 46% 

18% 13% 72,130 miles 10% 41%

Macroinvertebrate Index Riparian Disturbance Riparian Vegetative Cover

36% 30% 52%

23% 50% 24%

39% 20% 24%

Salinity Acidification 

O/E Taxa Loss 95% 89%

3% 5% 15% 38% 12% 32% 3% 2% 6%

0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

3%

2% 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
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Biological Condition

• The Macroinvertebrate Index reveals that 

39% of stream length in the Coastal Plains 

ecoregion is in poor condition, 23% is in 

fair or intermediate condition, and 36% is in 

good condition compared to least-disturbed 

reference condition. No data were available to 

evaluate 2% of the ecoregion’s stream length. 

• The O/E Taxa Loss results show that 65% of 

stream length in the Coastal Plains ecoregion 

has lost 10% or more of the macroinvertebrate 

taxa that are expected to occur, and 15% has 

lost more than 50% of taxa. These results 

also indicate that 32% of stream length has 

retained 90% of the groups or classes of 

organisms expected to occur based on leastdisturbed reference condition.

Indicators of Stress

Leading indicators of stress in the Coastal 

Plains ecoregion include total phosphorus, instream fish habitat, riparian vegetative cover, and 

streambed sediments. 

• Twenty-nine percent of stream length in the 

Coastal Plains ecoregion has high phosphorus 

concentrations, 13% has medium phosphorus 

concentrations, and 58% has low phosphorus 

concentrations based on least-disturbed 

reference condition. 

• Ten percent of the ecoregion’s stream length 

has high nitrogen concentrations, 18% has 

medium nitrogen concentrations, and 72% 

has low nitrogen concentrations based on 

least-disturbed reference condition. 

• Riparian disturbance, or evidence of human 

influence in the riparian zone, is at high levels 

in 20% of stream length, at medium levels 

in 50% of stream length, and at low levels in 

30% of stream length.

• Salinity is found at high or medium levels in 

5% of stream length, with the remaining 95% 

of stream length showing low levels for this 

indicator.

• Streambed sediments are rated poor in 22% of 

stream length in the Coastal Plains ecoregion, 

fair in 11% of stream length, and good in 

64% of stream length based on least-disturbed 

reference condition; no data were available to 

assess the remaining 3% of stream length.

• In-stream fish habitat is in poor condition in 

41% of stream length, fair in 13% of stream 

length, and good in 46% of stream length, 

based on least-disturbed reference condition. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 24% 

of stream length, fair condition for 24% of 

stream length, and good condition in the 

remaining 52% of stream length based on 

least-disturbed reference condition.

• In this ecoregion, the ANC is low enough to 

result in episodic acidification during rainfall 

in 6% of stream length. Another 5% of stream 

length has naturally lower pH.
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

65

Raisin River, MI, in the Upper Midwest 

ecoregion (Photo courtesy of the Great Lakes 

Environmental Center).

Upper Midwest Ecoregion

Physical Setting

The Upper Midwest ecoregion covers most 

of the northern half and southeastern part of 

Minnesota, two-thirds of Wisconsin, and almost 

all of Michigan. The land area of the Upper 

Midwest ecoregion comprises some 160,374 mi2

(5.3% of the United States). The river systems 

in this ecoregion empty into portions of the 

Great Lakes regional watershed and the upper 

Mississippi River watershed. Major river systems 

include the upper Mississippi River in Minnesota 

and Wisconsin; the Wisconsin, Chippewa, and 

St. Croix rivers in Wisconsin; and the Menominee 

and Escanaba rivers in Michigan. Streams in 

the Upper Midwest ecoregion typically drain 

relatively small catchments and empty directly 

into the Great Lakes or upper Mississippi River. 

These streams generally have steep gradients, but 

their topography and soils tend to slow runoff 

and sustain flow throughout the year. 

The total stream length represented in the 

WSA for the Upper Midwest ecoregion is 36,547 

wadeable stream miles. Sandy soils dominate these 

waterbodies, with relatively high water quality in 

streams supporting cold-water fish communities. 

Important waterbodies in this ecoregion include 

the Upper Mississippi River system and Lakes 

Superior, Michigan, Huron, and Erie. 

The glaciated terrain of this ecoregion typically 

consists of plains with some hill formations. 

Numerous lakes, rivers, and wetlands predominate 

in most areas. The climate is characterized by 

cold winters and relatively short, warm summers, 

with mean annual temperatures ranging from 

34 to 54 °F and annual precipitation in the 

20- to 47-inch range. Much of the land in this 

ecoregion is covered by national and state forests, 

and federal lands account for 15.5% of the area 

(roughly 25,000 mi2

). Based on satellite images in 

the 1992 NLCD, the distribution of land cover 

in this ecoregion is 40% forested, 34% planted/

cultivated, and 17% wetlands, with the remaining 

9% of the ecoregion comprised of other types of 

land cover.

Biological Setting

Vegetative cover for the Upper Midwest 

ecoregion is mixed boreal woodland, mixed 

oak-hickory associations, and conifers, as well as 

bog and moss barrens. The Great Lakes aquatic 

ecosystems are subject to increasing intrusion by 

invasive animal and plant species introduced by 

ocean shipping. These species include the zebra 

mussel, the round goby, the river ruffe, the spiny 

water flea, and Eurasian watermilfoil. 

Human Influence

The Upper Great Lakes portion of the Upper 

Midwest ecoregion was entirely forested in 
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66

pre-colonial times. Virtually all of the virgin forest 

was cleared in the 19th and early 20th centuries, 

and streams and rivers were greatly affected by 

the logging industry. The upper Mississippi River 

portion of the Upper Midwest ecoregion was also 

heavily influenced by logging and agriculture.

Major manufacturing, chemical, steel, and 

power production (e.g., coal, nuclear, oil) occur in 

the large metropolitan areas found in the Upper 

Midwest ecoregion. Other key economic activities 

are forestry, mining, and tourism. Agriculture 

includes dairy production, grain crops in the 

western areas, fruit production around the Great 

Lakes, and hay and cattle farming throughout 

the ecoregion. Pulp, paper, and board wood 

processing are prevalent throughout the northern 

parts of the ecoregion. The area includes the 

shipping ports at Duluth, MN, and Superior, WI, 

as well as cities like Marquette, MI, and Hibbing, 

MN, which were built up along with the mining 

industry. The Upper Peninsula of Michigan lies 

entirely within the Upper Midwest ecoregion, 

as does Minnesota’s Mesabi Range, the largest 

U.S. iron ore deposit. This area is subject to the 

environmental effects of mining operations. There 

are currently 112 active, 1 proposed, and 12 

deleted EPA Superfund National Priority List sites 

in this ecoregion.

The approximate population of this area is 

15,854,000, representing approximately 5% of 

the population of the United States. 

Summary of WSA Findings

A total of 56 random sites were sampled in the 

Upper Midwest ecoregion during the summer of 

2004 to characterize the condition of its wadeable 

streams. An overview of the WSA survey results 

for the Upper Midwest ecoregion is shown in 

Figure 29. These results may not be extrapolated 

to an individual state or stream within the 

ecoregion because the study design was not 

intended to characterize stream conditions at 

these finer scales. 

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Upper Midwest 

ecoregion said that some of the ecoregion’s leastdisturbed streams that serve as a benchmark for 

reference condition are influenced by some form 

of human activity or land use; however, most 

of the least-disturbed reference sites are streams 

in relatively undisturbed areas in the northern 

portion of the ecoregion. 

Biological Condition

• The Macroinvertebrate Index reveals that 

39% of stream length in the Upper Midwest 

ecoregion is in poor condition, 31% is in 

fair condition, and 28% is in good condition 

based on least-disturbed reference condition. 

• The O/E Taxa Loss results show that 54% of 

stream length in the Upper Midwest ecoregion 

has lost 10% or more of the macroinvertebrate 

taxa that are expected to occur, and 5% has 

lost more than 50% of taxa. These results 

also indicate that 45% of stream length has 

retained at least 90% of the groups or classes 

of organisms expected to occur based on leastdisturbed reference condition. 

Indicators of Stress

Leading indicators of stress in the Upper 

Midwest ecoregion include total phosphorus, total 

nitrogen, streambed sediments, and in-stream fish 

habitat.

• Thirty-eight percent of stream length in 

the Upper Midwest ecoregion has high 

phosphorus concentrations, 18% has medium 
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

67

phosphorus concentrations, and 42% has low 

phosphorus concentrations based on leastdisturbed reference condition.

• Twenty-one percent of the ecoregion’s stream 

length has high nitrogen concentrations, 

30% of stream length has medium nitrogen 

concentrations, and 48% of stream length has 

low nitrogen concentrations based on leastdisturbed reference condition.

• Riparian disturbance, or evidence of human 

influence in the riparian zone, is at high levels 

in 6% of stream length, at medium levels in 

45% of stream length, and at low levels in 

49% of stream length.

• Salinity is found at medium levels in 22% 

of stream length and at low levels in 77% of 

stream length. None of the steam length of the 

Upper Midwest ecoregion showed high levels 

for this indicator.

• Streambed sediments are rated poor in 50% of 

stream length, fair in 11%, and good in 37%; 

data for this indicator were not available for 

2% of stream length. 

• In-stream fish habitat is in poor condition in 

17% of stream length, fair in 69% of stream 

length, and good in 14% of stream length 

based on least-disturbed reference condition. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition in 13% of 

stream length, fair condition in 38% of stream 

length, and in good condition in 44% of 

stream length. 

• The effects of acidification are not noted for 

the Upper Midwest ecoregion.

Figure 29. WSA survey results for the Upper Midwest ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent the 

width of the 95% confidence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

Phosphorus Streambed Sediments

Nitrogen In-stream Fish Habitat 

Upper Midwest Ecoregion

36,547 miles

42% 37%

18% 11%

38% 50%

48% 14%

30% 69%

21% 17%

Macroinvertebrate Index Riparian Disturbance Riparian Vegetative Cover

28% 49% 44%

31% 45% 38%

39% 6% 13%

Salinity

77% O/E Taxa Loss 22% 96%

5% 31% 18% 45%

0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100

Percentage Stream Length Percentage Stream Length

Good

Fair

Poor

Not Assessed

Low

Medium

High

Not Assessed

2% 2%

1%

2% 4%

1%

1%

Percentage Stream Length

> 50% Taxa Loss 20–50% Taxa Loss

10–20% Taxa Loss < 10% Taxa Loss

Not Assessed

Good Fair Poor Not Assessed

For O/E Taxa Loss:

Acidification

100%

For Macroinvertebrate Index:
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

68

Temperate Plains Ecoregion

Physical Setting

The Temperate Plains ecoregion includes the 

open farmlands of Iowa; the eastern Dakotas; 

western Minnesota; portions of Missouri, Kansas, 

and Nebraska; and the flat farmlands of western 

Ohio, central Indiana, Illinois, and southeastern 

Wisconsin. The area of this ecoregion covers some 

342,200 mi2

 (11.4% of the United States), with 

approximately 7,900 mi2

 (2.3%) of land under 

federal ownership. The ecoregion’s terrain consists 

of smooth plains and numerous small lakes and 

wetlands. The climate is temperate, with fairly 

cold winters; hot, humid summers; and mean 

temperatures ranging from 36 to 55 °F. Annual 

precipitation in the Temperate Plains ecoregion 

ranges from 16 to 43 inches. 

Many of the rivers in this ecoregion drain 

into the Upper Mississippi and Ohio regional 

watersheds, and a few systems empty into the 

Great Lakes watershed near Toledo, OH; Saginaw, 

MI; Detroit, MI; and southeastern Wisconsin. 

Rivers are either supplied by snowmelt or 

groundwater. Rivers in the tall grass prairie start 

from prairie potholes and springs and are likely 

to be ephemeral (flowing for a short time after 

snowmelt or rainfall). The prairie rivers carry 

large volumes of fine sediments and tend to be 

turbid, wide, and shallow. The total stream length 

represented in the WSA for the Temperate Plains 

ecoregion is 100,879 wadeable stream miles. 

Based on satellite images in the 1992 NLCD, the 

distribution of land cover in this ecoregion is 9% 

forested and 76% planted/cultivated, with the 

remaining 15% of the ecoregion comprised of 

other types of land cover.

Biological Setting

Vegetation for the Temperate Plains ecoregion 

consists primarily of oak, hickory, elm, ash, beech, 

and maple, with increasing amounts of prairie 

grasses to the west. Rivers have rich fish fauna 

with many species, including minnows, darters, 

killifishes, catfishes, suckers, sunfishes, and black 

bass. Few species are endemic to the ecoregion.

Human Influence

Pre-settlement vegetation of the area was 

prairie grass and aspen parkland, but is now 

comprised of about 75% arable cultivated lands. 

This ecoregion is rich in agricultural production, 

including field crops such as corn, wheat, 

alfalfa, soybeans, flaxseed, and rye, along with 

vegetable crops such as peanuts and tomatoes. 

Hog and cattle production and processing are 

also prevalent. Crops and grazing have reduced 

Grey Horse Creek, OK, in the Temperate Plains 

ecoregion (Photo courtesy of Monty Porter).
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

69

natural riparian vegetation cover, increased 

sediment yield, and introduced pesticides and 

herbicides into the watershed. Conservation 

tillage — a reduced-cultivation method — has 

been implemented in about 50% of crop fields 

in the Maumee River Basin and in northwestern 

Ohio tributaries draining to Lake Erie. USGS 

findings from 1993–1998 in these rivers 

showed significant decreases in the amounts of 

suspended sediment. Rivers in the Temperate 

Plains ecoregion also tend to have high nitrogen 

concentrations due to nutrients from agriculture 

and from fertilizer applied to lawns and golf 

courses in urban areas. In Illinois, where land is 

intensively developed through urbanization and 

agriculture, more than 25% of all sizable streams 

have been channelized, and almost every stream 

in the state has at least one dam. 

Coal mining, petroleum and natural gas 

production, and zinc and lead mining occur 

across the Temperate Plains ecoregion. There are 

very active areas of manufacturing, steel production, and chemical production in the ecoregion’s 

urban centers, with especially high concentrations 

near Detroit, MI, and the industrial belt from 

Gary, IN, to Chicago, IL, and Milwaukee, WI. 

Industrial activities in these large urban centers 

have contributed sewage, toxic compounds, and 

silt to river systems. Heavy metals, 

organochlorines, and PCBs are especially 

prevalent and persistent river contaminants found 

in industrial areas; however, many rivers have 

improved from their worst state in the 1960s. 

There are currently 133 active, 17 proposed, and 

44 deleted EPA Superfund National Priority List 

sites in the Temperate Plains ecoregion.

The approximate population of this ecoregion 

is 38,399,000, representing approximately 13% 

of the U.S. population. 

Summary of WSA Findings

A total of 132 random sites were sampled 

during the summer of 2004 to characterize the 

condition of wadeable streams throughout the 

Temperate Plains ecoregion. An overview of the 

WSA survey results for the Temperate Plains 

ecoregion is shown in Figure 30. These results 

may not be extrapolated to an individual state or 

stream within the ecoregion because the study 

design was not intended to characterize stream 

conditions at these finer scales.

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Temperate Plains 

ecoregion said that it is hard to find high-quality 

reference sites in the ecoregion because even 

the least-disturbed streams are influenced by a 

long history of land use. Extensive agriculture 

and development have influenced virtually all 

waterbodies in this ecoregion. 

Biological Condition

• The Macroinvertebrate Index reveals that 

37% of stream length in the Temperate Plains 

ecoregion is in poor condition, 36% is in 

fair condition, and 26% is in good condition 

compared to least-disturbed reference 

condition. 

• The O/E Taxa Loss results show that 39% 

of stream length in the Temperate Plains 

ecoregion has lost 10% or more of the 

macroinvertebrate taxa that are expected to 

occur, and 10% has lost more than 50% of 

taxa. These results also indicate that 58% of 

stream length has retained 90% of the groups 

or classes of organisms expected to occur based 

on least-disturbed reference condition.
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

70

Indicators of Stress

Leading indicators of stress in the Temperate 

Plains ecoregion include total nitrogen, riparian 

disturbance, in-stream fish habitat, and riparian 

vegetative cover. 

• Approximately 12% of stream length in the 

Temperate Plains ecoregion has high 

phosphorus concentrations, 13% has medium 

phosphorus concentrations, and 74% has low 

phosphorus concentrations based on leastdisturbed reference condition. 

• Approximately 41% of the ecoregion’s stream 

length has high nitrogen concentrations, 17% 

has medium nitrogen concentrations, and 

41% has low nitrogen concentrations based on 

least-disturbed reference condition. 

• Riparian disturbance for this ecoregion is at 

high levels in approximately 38% of stream 

length, at medium levels in 58% of stream 

length, and at low levels in 3% of stream 

length.

• Salinity is found at high levels in 2% of stream 

length, at medium levels in 13% of stream 

length, and at low levels in 84% of stream 

length.

• Excess streambed sediments affect streams in 

the Temperate Plains ecoregion to a lesser 

extent than other physical stressors. Streambed 

sediments are rated poor in 20% of stream 

length in this ecoregion, fair in 12%, and good 

in 67% based on least-disturbed reference 

condition. 

Figure 30. WSA survey results for the Temperate Plains ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent the 

width of the 95% confidence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

1%

1%

Phosphorus Streambed Sediments

74% 67%

13% 12%

12% 20%

1% 1%

Nitrogen In-stream Fish Habitat

Temperate Plains Ecoregion 41% 41%

17% 19%

100,879 miles 39%

1% 1%

Riparian Disturbance 

26% 3%

36% 58%

37% 38% 1%

Salinity 

84%

13%

2% 10% 17% 12% 58% 2% 1%

41%

Riparian Vegetative Cover

53%

17%

26%

3%

Acidification 

99%

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

Macroinvertebrate Index 

O/E Taxa Loss 

0 20 40 60 80 100 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
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Chapter 3 Wadeable Streams Assessment Ecoregion Results

71

• In-stream fish habitat is in poor condition in 

39% of stream length, fair in 19% of stream 

length, and good in 41% of stream length 

based on least-disturbed reference condition. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 26% 

of stream length, fair condition for 17% of 

stream length, and good condition for 53% of 

stream length.

• The effects of acidification are not noted for 

the Temperate Plains ecoregion. 

Southern Plains Ecoregion

Physical Setting

The Southern Plains ecoregion covers 

approximately 405,000 mi2

 (13.5% of the 

United States) and includes central and northern 

Texas; most of western Kansas and Oklahoma; 

and portions of Nebraska, Colorado, and New 

Mexico. The terrain is a mix of smooth and 

irregular plains interspersed with tablelands 

and low hills. The Arkansas, Platte, White, 

Red, and Rio Grande rivers flow through this 

ecoregion, and most of the great Ogallala aquifer 

lies underneath this ecoregion. The total stream 

length represented in the WSA for the Southern 

Plains ecoregion is 19,263 wadeable stream miles. 

Most of the land use is arable and arable 

with grazing, with desert or semi-arid grazing 

land in the south. Based on satellite images 

in the 1992 NLCD, the distribution of land 

cover in this ecoregion is 45% grassland, 32% 

planted/cultivated, and 14% shrubland, with 

the remaining 9% of the ecoregion comprised of 

other types of land cover. Federal land ownership 

in this ecoregion totals about 11,980 mi2

 or 

approximately 3% of the total, the lowest share 

of all WSA aggregate ecoregions. The climate is 

dry temperate, with the mean annual temperature 

ranging from 45 to 79 °F. Annual precipitation 

for the ecoregion is between 10 and 30 inches. 

Biological Setting

Vegetative cover in the northern portion of 

this ecoregion is mainly short prairie grasses such 

as buffalo grass, while in the southern portion, 

grasslands with mesquite, juniper, and oak woody 

vegetation are common. Coastal vegetation in the 

southern Plains ecoregion is typically more salttolerant in nature.

Commission Creek, OK, in the Southern Plains 

ecoregion (Photo courtesy of Monty Porter). 
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Human Influence

The Great Prairie grasslands, which once 

covered much of the Southern Plains ecoregion, 

are the most altered and endangered large 

ecosystem in the United States. About 90% of 

the original tall grass prairie was replaced by 

other vegetation or land uses. Agriculture is an 

important economic activity in this ecoregion and 

includes sorghum, wheat, corn, sunflower, bean, 

and cotton production. Livestock production 

and processing is prevalent, especially goats, 

sheep, and cattle. The ecoregion contains a 

sizable portion of U.S. petroleum and natural 

gas production in Oklahoma, Kansas, and Texas. 

Electricity in this ecoregion is generated almost 

exclusively with gas-fired power plants. Some 

uranium and zinc mining is found in Oklahoma 

and the Texas panhandle. There are currently 

39 active, 5 proposed, and 14 deleted EPA 

Superfund National Priority List sites in this 

ecoregion.

The approximate population in this ecoregion 

is 18,222,000, representing roughly 6% of the 

population of the United States.

Summary of WSA Findings

A total of 49 random sites were sampled during 

the summer of 2004 to characterize the condition 

of wadeable streams throughout the Southern 

Plains ecoregion. An overview of the WSA survey 

results for the ecoregion is shown in Figure 31. 

These results may not be extrapolated to an 

individual state or stream within the ecoregion 

because the study design was not intended to 

characterize stream conditions at these finer scales. 

Figure 31. WSA survey results for the Southern Plains ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent the 

width of the 95% confidence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

Phosphorus Streambed Sediments 

Nitrogen In-stream Fish Habitat 

Southern Plains Ecoregion 

19,263 miles 

45% 52%

7% 18%

48% 30%

34% 35%

30% 23%

36% 42%

Riparian Disturbance Riparian Vegetative Cover

22% 14% 24%

20% 67% 40%

54% 19% 36%

Salinity Acidification 

57% 100% 

21%

22% 15% 15% 20% 42% 8% 

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

Macroinvertebrate Index 

4%

O/E Taxa Loss 

0 20 40 60 80 100 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
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During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Southern Plains 

ecoregion said that no undisturbed streams 

remain in the ecoregion. The least-disturbed 

streams are those that retain natural configuration 

and have riparian buffer zones. 

Biological Condition

• The Macroinvertebrate Index reveals that 

54% of stream length in the Southern Plains 

ecoregion is in poor condition, 20% is in 

fair condition, and 22% is in good condition 

compared to least-disturbed reference 

condition. There are no data for the remaining 

4% of stream length. 

• The O/E Taxa Loss results show that 50% of 

stream length in the Southern Plains ecoregion 

has lost 10% or more of the macroinvertebrate 

taxa expected to occur, and 15% has lost more 

than 50% of taxa. These results also indicate 

that 42% of the ecoregion’s stream length 

has retained 90% of the groups or classes of 

organisms expected to occur based on leastdisturbed reference condition.

Indicators of Stress

The most widespread indicators of stress 

in the Southern Plains ecoregion include total 

phosphorus, total nitrogen, in-stream fish habitat, 

and riparian vegetative cover. 

• Forty-eight percent of stream length in 

the Southern Plains ecoregion has high 

phosphorus concentrations, 7% has medium 

phosphorus concentrations, and 45% has low 

phosphorus concentrations based on leastdisturbed reference condition.

• Approximately 36% of the ecoregion’s stream 

length has high nitrogen concentrations, 30% 

has medium nitrogen concentrations, and 

34% has low nitrogen concentrations based on 

least-disturbed reference condition. 

• Riparian disturbance in this ecoregion is at 

high levels in 19% of stream length. The 

majority of stream length (67%) has medium 

levels of riparian disturbance, and only 14% 

has low levels for this indicator. 

• Salinity is found at high levels in 22% of 

stream length, at medium levels in 21% of 

stream length, and at low levels in 57% of 

stream length.

• Streambed sediments are rated poor in 30% of 

stream length, fair in 18%, and good in 52% 

based on least-disturbed reference condition.

• In-stream fish habitat is in poor condition in 

42% of stream length, fair in 23% of stream 

length, and good in 35% of stream length 

based on least-disturbed reference condition. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 36% of 

stream length, in fair condition for 40% of 

stream length, and good condition for 24% of 

stream length. 

• The effects of acidification are not noted for 

the Southern Plains ecoregion.
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Northern Plains Ecoregion

Physical Setting

The Northern Plains ecoregion covers approximately 205,084 mi2

 (6.8% of the United States), 

including the western Dakotas, Montana east of 

the Rocky Mountains, northeast Wyoming, and 

a small section of northern Nebraska. Federal 

lands account for 52,660 mi2

 or a relatively large 

(25.7%) share of the total area. The Great Prairie 

grasslands were also an important feature of this 

ecoregion, but about 90% of these grasslands have 

been replaced by other vegetation or land use. The 

ecoregion’s terrain is irregular plains interspersed 

with tablelands and low hills. This ecoregion is 

the heart of the Missouri River system and is 

almost exclusively within the Missouri River’s 

regional watershed. The total stream length 

represented in the WSA for the Northern Plains 

ecoregion is 13,445 wadeable stream miles.

Land use is arable with grazing or semiarid grazing. Based on satellite images in the 

1992 NLCD, the distribution of land cover 

in this ecoregion is 56% grassland and 30% 

planted/cultivated, with the remaining 14% of 

the ecoregion comprised of other types of land 

cover. Significant wetlands are also found in the 

Nebraska Sandhills area. The climate is dry and 

continental, characterized by short, hot summers 

and long, cold winters. Temperatures average 36 to 

46 °F, and annual precipitation totals range from 

10 to 25 inches. High winds are an important 

climatic factor in this ecoregion. It is also subject 

to periodic, intense droughts and frosts.

Biological Setting

The predominant vegetative cover for the 

Northern Plains ecoregion was formerly native 

short prairie grasses, such as wheat grass and 

porcupine grass, but now cropland is much more 

prevalent. 

Wolf Creek, McCook County, SD, in the Northern Plains ecoregion

(Photo courtesy of Dynamac Corp). 
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Human Influence

Human economic activity is primarily 

agriculture, including cattle and sheep grazing, 

as well as the growing of wheat, barley, and 

sugar beets. Coal mining occurs in the North 

Dakota, Montana, and Wyoming portions of 

the ecoregion. Petroleum and gas production has 

grown considerably in the Cut Bank region in 

north-central Montana. There are several large 

Indian reservations in this ecoregion, including 

the Pine Ridge, Standing Rock, and Cheyenne 

reservations in South Dakota and the Blackfeet, 

Crow, and Fort Peck reservations in Montana. 

There are currently four active and one proposed 

EPA Superfund National Priority List sites in this 

ecoregion.

The approximate population of this ecoregion 

is relatively small at 1,066,000, or 0.4% of the 

population of the United States.

Summary of WSA Findings

A total of 98 random sites were sampled during 

the summers of 2000–2004 to characterize the 

condition of wadeable streams throughout the 

Northern Plains ecoregion. An overview of the 

WSA survey results for the ecoregion is shown in 

Figure 32. These results may not be extrapolated 

to an individual state or stream within the 

ecoregion because the study design was not 

intended to characterize stream conditions at 

these finer scales. 

Figure 32. WSA survey results for the Northern Plains ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent the 

width of the 95% confidence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

Phosphorus Streambed Sediments

54% 50%

13% 14%

33% 33%

Nitrogen In-stream Fish Habitat 

60% 34% Northern Plains Ecoregion 21% 21%

13,445 miles 18% 45%

Riparian Disturbance Riparian Vegetative Cover

30% 3% 28%

13% 66% 22%

50% 31% 50%

Salinity Acidification 

40% 100% 

22%

38% 12% 16% 6% 60% 7% 

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

3%

Macroinvertebrate Index 

7%

O/E Taxa Loss 

0 20 40 60 80 100 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
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During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Northern Plains 

ecoregion said that although the ecoregion 

has relatively few undisturbed streams, the 

majority are in areas of low-level agriculture and 

pastureland. 

Biological Condition

• The Macroinvertebrate Index reveals that 

50% of stream length in the Northern Plains 

ecoregion is in poor condition, 13% is in 

fair condition, and 30% is in good condition 

compared to least-disturbed reference 

condition. There are no data for the remaining 

7% of stream length. 

• The O/E Taxa Loss results show that 34% of 

stream length has lost 10% or more of the 

macroinvertebrate taxa expected to occur, 

and 12% has lost more than 50% of taxa. 

These results also indicate that 60% of the 

ecoregion’s stream length has retained 90% of 

the groups or classes of organisms expected 

to occur based on least-disturbed reference 

condition.

Indicators of Stress

The most widespread indicators of stress in 

the Northern Plains ecoregion include riparian 

vegetative cover, in-stream fish habitat, riparian 

disturbance, and salinity. 

• Thirty-three percent of stream length in 

the Northern Plains ecoregion has high 

phosphorus concentrations, 13% has medium 

phosphorus concentrations, and 54% has low 

phosphorus concentrations based on leastdisturbed reference condition.

• Eighteen percent of the ecoregion’s stream 

length has high nitrogen concentrations, 21% 

has medium nitrogen concentrations, and 

60% has low nitrogen concentrations based on 

least-disturbed reference condition. 

• Riparian disturbance in the Northern Plains 

ecoregion is at high levels in 31% of stream 

length, at medium levels in 66% of stream 

length, and at low levels in 3% of stream 

length.

• Salinity is a significant stressor in the Northern 

Plains. Salinity is high in 38% of stream 

length, medium in 22% of stream length, and 

low in 40% of stream length. 

• Streambed sediments are rated poor in 33% 

of stream length in the Northern Plains 

ecoregion, fair in 14%, and good in 50% 

based on least-disturbed reference condition; 

data for this indicator were unavailable for 3% 

of stream length. 

• In-stream fish habitat is in poor condition in 

45% of stream length, fair in 21% of stream 

length, and good in 34% of stream length 

based on least-disturbed reference condition. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 50% of 

stream length, in fair condition for 22% of 

stream length, and in good condition for 28% 

of stream length. 

• The effects of acidification are not noted for 

the Northern Plains ecoregion.
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77

Western Mountains 

Ecoregion

Physical Setting

The Western Mountains ecoregion includes 

the Cascade, Sierra Nevada, and Pacific Coast 

ranges in the coastal states; the Gila Mountains 

in the southwestern states; and the Bitteroot 

and Rocky mountains in the northern and 

central mountain states. This ecoregion covers 

approximately 397,832 mi2

, with about 297,900 

mi2

 or 74.8% classified as federal land — the 

highest proportion of federal property among all 

the 9 aggregate ecoregions. The terrain of this 

area is characterized by extensive mountains and 

plateaus separated by wide valleys and lowlands. 

Coastal mountains are transected by numerous 

fjords and glacial valleys, are bordered by coastal 

plains, and include important estuaries along 

the ocean margin. Soils are mainly nutrient-poor 

forest soils. Based on satellite images in the 1992 

NLCD, the distribution of land cover in this 

ecoregion is 59% forested, 19% shrubland, and 

13% grassland, with the remaining 9% of the 

ecoregion comprised of other types of land cover.

The headwaters and upper reaches of the 

Columbia, Sacramento, Missouri, and Colorado 

river systems all occur in this ecoregion. Smaller 

rivers share many characteristics, starting as steep 

mountain streams with staircase-like channels 

and steps and plunge pools, with riffles and 

pools appearing as slope decreases. Upper river 

reaches experience debris flows and landslides 

when shallow soils become saturated by rainfall or 

snowmelt. The total stream length represented in 

the WSA for the Western Mountains ecoregion is 

126,436 wadeable stream miles. 

Unnamed tributary to Lake Creek, Chelan County, 

WA, in the Western Mountains ecoregion (Photo 

courtesy of the Washington Department of Ecology).

The climate is sub-arid to arid and mild in 

southern lower valleys, and humid and cold at 

higher elevations. The wettest climates of North 

America occur in the marine coastal rain forests of 

this ecoregion. Mean annual temperatures range 

from 32 to 55 °F, and annual precipitation ranges 

from 16 to 240 inches. 
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78

Biological Setting

Rivers in this ecoregion drain dense forested 

catchments and contain large amounts of woody 

debris that provide habitat diversity and stability. 

Rivers reaching the Pacific Ocean historically had 

large runs of salmon and trout, including pink, 

chum, sockeye, coho, and chinook salmon, as well 

as cutthroat and steelhead trout. Many of these 

anadromous fish populations have been reduced 

since the time of European settlement due to the 

effects of overfishing, introduced species, flow 

regulations, and dams. Spawning habitats in 

stream pools have been drastically reduced due to 

increased sediments from logging, mining, and 

other land use changes.

Human Influence

Deforestation and urbanization continue to 

alter stream habitats in the mountainous west. 

The Western Mountains riparian ecosystems first 

encountered pressure from grazing and mining 

from the mid-1800s to about 1910 and then from 

the logging roads and fire management practices 

that occur to the present day. 

Placer mining, which disrupts stream sediment 

habitats, was once widespread in the Western 

Mountains ecoregion. Particularly damaging 

in mountainous areas was the introduction of 

mercury, which was used extensively in placer 

mining for gold. Toxic contaminants from 

mining also include arsenic, antimony, copper, 

chromium, cadmium, nickel, lead, selenium, 

silver, and zinc. In addition to mining, other 

activities such as logging, grazing, channelization, 

dams, and diversions in the Sierra Nevada 

area also significantly impacted rivers and 

streams. Introduced fish provided further stress, 

with several native fish species threatened or 

endangered. 

The principal economic activities in this 

ecoregion are high-tech manufacturing, wood 

processing, international shipping, U.S. naval 

operations, commercial fishing, tourism, grazing, 

and timber harvesting. Hydroelectric power 

generation is prevalent in the Pacific Northwest 

area and California. Bauxite mining also occurs in 

the Pacific Northwest portions of the ecoregion. 

There are currently 74 active, 7 proposed, and 

22 deleted EPA Superfund National Priority List 

sites in the Western Mountains ecoregion.

The approximate population in the Western 

Mountains ecoregion is 9,742,192, representing 

approximately 3% of the population of the 

United States.

Summary of WSA Findings

A total of 529 random sites were sampled 

during the summers of 2000–2004 to characterize 

the condition of wadeable streams throughout 

the Western Mountains ecoregion. This ecoregion 

had the greatest number of sample sites because 

all the western states enhanced the scale of the 

national survey by including additional random 

sites. Although there are enough sites to develop 

state-scale estimates of condition, this report did 

not produce those estimates. The individual states 

are analyzing the survey results in the context of 

their own water quality standards and assessment 

methodologies. An overview of the WSA survey 

results for the Western Mountains ecoregion is 

shown in Figure 33. These results may not be 

extrapolated to an individual state or stream 

within the ecoregion. 

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Western Mountains 

ecoregion said that many least-disturbed streams 
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79

in the ecoregion are of relatively high quality; 

however, some of these streams have mining and 

logging impacts, leading to reference conditions 

of varying degrees of quality. 

Biological Condition

• The Macroinvertebrate Index reveals that 25% 

of stream length in the Western Mountains 

ecoregion is in poor condition, 28% is in 

fair condition, and 46% is in good condition 

compared to least-disturbed reference 

condition. There are no data for about 1% of 

stream length. 

• The O/E Taxa Loss results show that 33% of 

stream length has lost 10% or more of the 

macroinvertebrate taxa expected to occur, and 

5% has lost more than 50% of taxa. These 

results indicate that 63% of stream length 

has retained 90% of the groups or classes of 

organisms expected to occur based on leastdisturbed reference condition.

Indicators of Stress

The most widespread indicators of stress in 

the Western Mountains ecoregion include total 

nitrogen, total phosphorus, riparian disturbance, 

and streambed sediments. 

• Sixteen percent of stream length in the 

Western Mountains ecoregion has high 

phosphorus concentrations, 25% has medium 

phosphorus concentrations, and 59% has low 

phosphorus concentrations based on leastdisturbed reference condition.

Figure 33. WSA survey results for the Western Mountains ecoregion (U.S. EPA/WSA). Bars show the 

percentage of stream length within a condition class for a given indicator. Lines with brackets represent the 

width of the 95% confidence interval around the percent of stream length. Percents may not add up to 100 

because of rounding.

Phosphorus Streambed Sediments 

59%

25%

16%

Nitrogen In-stream Fish Habitat 

Western Mountains Ecoregion 54% 70%

28% 20% 126,436 miles 17% 9%

Riparian Vegetative Cover

46% 59%

28% 32%

9% 25%

Riparian Disturbance 

39%

47%

14%

Salinity Acidification 

97% 99% 

3%

5% 18% 10% 63% 4% 1%

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

Macroinvertebrate Index 

O/E Taxa Loss 

0 20 40 60 80 100 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

63%

22%

14%

1%

1%

For Macroinvertebrate Index: 
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• Seventeen percent of the ecoregion’s stream 

length has high nitrogen concentrations, 28% 

has medium nitrogen concentrations, and 

54% has low nitrogen concentrations based on 

least-disturbed reference condition. 

• Riparian disturbance, or evidence of human 

influence in the riparian zone, is at high levels 

in 14% of stream length, at medium levels 

in 47% of stream length, and at low levels in 

39% of stream length.

• Levels of salinity are medium in 3% of stream 

length and low in 97% of stream length. 

None of the stream length for the Western 

Mountains ecoregion had high levels of 

salinity.

• Streambed sediments are rated poor in 14% of 

stream length in this ecoregion, fair in 22%, 

and good in the remaining 63%.

• In-stream fish habitat is in poor condition in 

9% of stream length, fair in 20% of stream 

length, and good in 70% of stream length. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition for 9% of 

stream length, in fair condition for 32% of 

stream length, and in good condition for 59% 

of steam length.

• Acidification is rated poor in nearly 1% of 

stream length and good in 99% of stream 

length. 

Fishing and tourism are important economic activities in the Western Mountains 

ecoregion (Photo courtesy of Ron Nichols, U.S. Department of Agriculture National 

Resources Conservation Service).
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Xeric Ecoregion

Physical Setting

The Xeric ecoregion covers the largest area of 

all WSA aggregate ecoregions and includes the 

most total land under federal ownership. This 

ecoregion covers portions of eleven western states 

and all of Nevada for a total of about 636,583 

mi2

 (21.2% of the United States). Some 453,000 

mi2

 or 71.2% of the land is classified as federal 

lands, including large tracts of public land, 

such as the Grand Canyon National Park, Big 

Bend National Park, and the Hanford Nuclear 

Reservation. Tribal lands include the Navajo, 

Hopi, and Yakima reservations. Based on satellite 

images in the 1992 NLCD, the distribution of 

land cover in this ecoregion is 61% shrubland and 

15% grassland, with the remaining 24% of the 

ecoregion comprised of other types of land cover.

The Xeric ecoregion is comprised of a mix 

of physiographic features, including plains with 

hills and low mountains, high-relief tablelands, 

piedmont, high mountains, and intermountain 

basins and valleys. The ecoregion includes the 

flat to rolling topography of the Columbia/Snake 

River Plateau; the Great Basin; Death Valley; 

and the canyons, cliffs, buttes, and mesas of the 

Colorado Plateau. All of the non-mountainous 

area of California falls in the Xeric ecoregion and 

is distinguished by a mild Mediterranean climate, 

agriculturally productive valleys, and large 

metropolitan areas. 

This ecoregion’s relatively limited surface 

water supply contributes to the Upper and Lower 

Colorado, Great Basin, California, Rio Grande, 

and Pacific Northwest regional watersheds. Large 

rivers flow all year, are supplied by snowmelt, 

West Clear Creek, Yavapai County, AZ, in the Xeric ecoregion 

(Photo courtesy of the Arizona Game and Fish Department/USGS).
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82

and peak in early summer. Small rivers in this 

ecoregion are mostly ephemeral. Most rivers are 

turbid because they drain erodable sedimentary 

rock in a dry climate, where sudden rains flush 

sediments down small rivers. Rivers are often 

subject to rapid change due to flash floods and 

debris flows. In southern areas, dry conditions 

and water withdrawals produce internal drainages 

that end in saline lakes or desert basins without 

reaching the ocean (e.g., Utah’s Great Salt Lake). 

The total stream length represented in the WSA 

for the Xeric ecoregion is 25,989 wadeable stream 

miles. 

The Xeric ecoregion’s climate varies widely 

from warm and dry to temperate, with mean 

annual temperatures ranging from 32 to 75 °F 

and annual precipitation in the 2- to 40-inch 

range. The dry weather in the Sonoran, Mojave, 

and Chihuahuan deserts is created by the rain 

shadows cast by the mountains to the west and is 

punctuated by heavy, isolated episodic rainfalls.

Biological Setting

Rivers create a riparian habitat oasis for plants 

and animals in the dry Xeric ecoregion areas. 

Many fish are endemic, are restricted to the 

Colorado River basin, and have evolved to cope 

with warm, turbid waters. Examples include 

the humpback chub, bonytail chub, Colorado 

pikeminnow, roundtail chub, razorback sucker, 

Colorado squawfish, Pyramid Lake cui-ui, and 

Lahontan cutthroat trout. Most of these fish 

are threatened or endangered as a result of flow 

regulations from dams, water withdrawals, and 

introduced non-native species. Threatened species 

of fish in desert areas include the Sonora chub 

and beautiful shiner. 

Human Influence

Impacts to the Xeric ecoregion riparian 

habitats have been heavy in the past 250 years 

because of water impoundment and diversion; 

groundwater and surface water extraction; grazing 

and agriculture; and mining, road development, 

and heavy recreational demand. Both the leastaltered and most-altered pre-settlement natural 

vegetation types are found in this ecoregion. 

Riparian habitats in this ecoregion have also 

been widely impacted by invasive species and 

contamination from agriculture and urban runoff. 

Big rivers in the southwestern canyon regions 

were altered due to large dam construction 

and large-scale water-removal projects for cities 

and agriculture, with attendant small streams 

that experience cycles of draining and filling in 

response to grazing, groundwater withdrawal, 

and urbanization. In many desert areas, 

dissolved solids such as boron, molybdenum, 

and organophosphates leach from desert soils 

into irrigation waters. Almost every tributary in 

California’s Central Valley has been altered by 

canals, drains, and other waterways. 

Principal economic activities include recreation 

and tourism; mining; agriculture; grazing; 

manufacturing and service industries; agriculture 

and food processing; aerospace and defense 

industries; and automotive-related industries. 

Petroleum production is prevalent in California. 

Agriculture includes production of a wide range 

of crops, from wheat, dry peas, lentils, and 

potatoes to grapes and cotton. Large agricultural 

irrigation projects include the Salt and Gila valleys 

and the Imperial and Central valleys in California. 

There are currently 139 active, 6 proposed, and 

24 deleted EPA Superfund National Priority List 

sites in this ecoregion. 
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83

The total population in the Xeric ecoregion 

is the third largest of all WSA ecoregions at 

approximately 46,800,000 people, or 16% of the 

population of the United States.

Summary of WSA Findings

A total of 176 random sites were sampled 

during the summers of 2000–2004 to characterize 

the condition of wadeable streams throughout the 

Xeric ecoregion. An overview of the WSA survey 

results for the Xeric ecoregion is shown in Figure 

34. These results may not be extrapolated to an 

individual state or stream within the ecoregion. 

During a series of WSA workshops conducted 

to evaluate assessment results, professional 

biologists working in the Xeric ecoregion said that 

many of the perennial, least-disturbed streams in 

this ecoregion have been influenced by past and 

current human activities. 

Biological Condition

• The Macroinvertebrate Index reveals that 39% 

of stream length in the Xeric ecoregion is in 

poor condition compared to least-disturbed 

reference condition, 15% is in fair condition, 

and 42% is in good condition. There are no 

data for about 4% of stream length. 

• The O/E Taxa Loss results show that 60% of 

stream length in the Xeric ecoregion has lost 

10% or more of the macroinvertebrate taxa 

expected to occur and 15% has lost more than 

50% of taxa. These results also indicate that 

34% of stream length has retained 90% of the 

groups or classes of organisms expected to occur 

based on least-disturbed reference condition.

Figure 34. WSA survey results for the Xeric ecoregion (U.S. EPA/WSA). Bars show the percentage of 

stream length within a condition class for a given indicator. Lines with brackets represent the width of the 95% 

confidence interval around the percent of stream length. Percents may not add up to 100 because of rounding.

Phosphorus Streambed Sediments 

60% 48%

10% 17%

29% 32%

Nitrogen In-stream Fish Habitat 

37% Xeric Ecoregion 47%

26% 25%

25,989 miles 36% 27%

Riparian Vegetative Cover

42% 49%

15% 21%

39% 28%

Acidification 

99%

15% 35% 10% 34% 5% 

Riparian Disturbance 

15%

40%

44%

Salinity 

56%

29%

13%

0 20 40 60 80 100 0 20 40 60 80 100 

Percentage Stream Length Percentage Stream Length 

Good 

Fair 

Poor 

Not Assessed 

Low 

Medium 

High 

Not Assessed 

1% 3%

1% 1%

Macroinvertebrate Index 

4% 1% 2%

O/E Taxa Loss 

1% 1%

0 20 40 60 80 100 

Percentage Stream Length 

> 50% Taxa Loss 20–50% Taxa Loss 

10–20% Taxa Loss < 10% Taxa Loss 

Not Assessed 

Good Fair Poor Not Assessed 

For O/E Taxa Loss: 

For Macroinvertebrate Index: 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 3 Wadeable Streams Assessment Ecoregion Results

84

Indicators of Stress

The leading indicators of stress in the Xeric 

ecoregion include riparian disturbance, total 

nitrogen, streambed sediments, and in-stream fish 

habitat. 

• Twenty-nine percent of stream length in 

the Xeric ecoregion has high phosphorus 

concentrations, 10% has medium phosphorus 

concentrations, and 60% has low phosphorus 

concentrations based on least-disturbed 

reference condition.

• Nitrogen is the leading chemical stressor in the 

Xeric region. Approximately 36% of stream 

length has high nitrogen concentrations, 26% 

has medium nitrogen concentrations, and 

37% has low nitrogen concentrations based on 

least-disturbed reference condition.

• Riparian disturbance, or evidence of human 

influence in the riparian zone, is the leading 

physical stressor for the Xeric ecoregion. 

Riparian disturbance in this ecoregion is 

at high levels in 44% of stream length, at 

medium levels in 40% of stream length, and at 

low levels in 15% of stream length.

• Salinity is rated high in 13% of stream length 

and medium in 29%, with 56% of stream 

length showing low levels of this indicator. 

Data for this indicator were unavailable for 

approximately 1% of stream length. 

• Streambed sediments are rated poor in 32% 

of stream length in the Xeric ecoregion, fair in 

17%, and good in 48%; data on this indicator 

were unavailable for 3% of stream length. 

• In-stream habitat is in poor condition in 

27% of stream length, fair in 25%, and good 

in 47% based on least-disturbed reference 

condition; data were unavailable for 1% of 

stream length. 

• Vegetative cover in the riparian zone along 

stream banks is in poor condition in 28% of 

stream length, in fair condition in 21% of 

stream length, and in good condition in 49% 

of stream length. 

• The effects of acidification are not noted for 

the Xeric ecoregion.

The Xeric ecoregion is 

comprised of a mix of 

physiographic features, 

including plains with 

hills and low mountains, 

high-relief tablelands, 

piedmont, high mountains, 

and intermountain 

basins and valleys (Photo 

courtesy of Tim McCabe, U.S. 

Department of Agricultural 

Natural Resources 

Conservation Service).
Chapter 4

Summary and Next Steps

Photo courtesy of Jeffrey Cole
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 4 Summary and Next Steps

86

Summary and Next 

Steps

Summary 

The United States covers an enormous and 

diverse landscape, and not surprisingly, the 

biological condition of the nation’s streams varies 

widely geographically. Overall, 42% percent of 

the nation’s stream length is in poor biological 

condition compared to least-disturbed reference 

condition in each of the WSA ecoregions. 

The Eastern Highlands region has the largest 

proportion of streams in poor biological 

condition (52%), whereas the West has the lowest 

proportion (27%). In the Plains and Lowlands 

region, 40% of stream length is in poor biological 

condition. 

Stream miles, represented as stream length, 

are not evenly distributed across the country. 

The densest coverage of perennial streams in 

the lower 48 states is in the Eastern Highlands 

region, which has approximately 276,362 miles 

of perennial streams and the smallest land area of 

the three major regions. The Plains and Lowlands 

region, which covers the largest portion of the 

United States, has 242,264 miles of perennial 

streams. The West has 152,425 miles of streams. 

It is important to evaluate the survey results in 

terms of both stream length percentages and 

absolute stream miles in each condition class. For 

example, the percentage of stream length in good 

condition varies dramatically between the West 

(45%) and Plains and Lowlands regions (29%); 

however, if these percentages are converted to 

stream miles, the West has 68,672 miles in good 

condition, whereas the Plains and Lowlands 

region has 70,257 miles in good condition.

The WSA fi nds that the most widespread 

or common stressors are elevated levels of the 

nutrients nitrogen and phosphorus, riparian 

disturbance, and excess streambed sediments. 

Nationally, 32% of stream length (213,394 miles) 

has high concentrations of nitrogen compared 

to least-disturbed reference conditions, and 

31% (207,355 miles) has high concentrations of 

phosphorus. Twenty-six percent of the nation’s 

stream length (171,118 miles) has high levels 

of riparian disturbance (e.g., human infl uence 

along the riparian zone), and 25% (167,092 

miles) has streambed sediment characteristics 

in poor condition. Analysis of the association 

between stressors and biological condition fi nds 

that high levels of nutrients and excess streambed 

sedimentation more than double the risk of poor 

biological condition. 

The WSA provides the fi rst nationally 

consistent baseline of the condition of the 

nation’s streams. This baseline will be used 

in future assessments to evaluate changes in 

conditions and to provide insights as to the 

effectiveness of water resource management 

actions. Highlight: Acidifi cation Trends and the 

Clean Air Act illustrates how this type of survey 

can be used to evaluate the effectiveness of 

management actions on improving water quality. 

States, EPA, and other partners plan to use this 

approach to implement large-scale assessments of 

lakes in 2007 and similar assessments of rivers, 

wetlands, and coastal waters in future years.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 4 Summary and Next Steps

87

Highlight

Acidification Trends and the Clean Air Act

Although this WSA provides a snapshot of the current conditions in the nation’s streams, future 

surveys will allow us to detect trends in stream conditions and in the stressors that affect them. One 

example in which probability-based survey designs were implemented repeatedly over the course of 

10 years has been the evaluation of the responsiveness of acid-sensitive lakes and streams to changes 

in policy and management actions. Title IV of the 1990 Clean Air Act Amendments (CAAA) set target 

reductions for sulfur and nitrogen emissions from industrial sources as a means of reducing the 

acidity in deposition. One of the intended effects of the reductions was to decrease the acidity of 

low-alkalinity waters. A 2003 EPA report by Stoddard et al., assessed recent changes in surface water 

chemistry in the northern and eastern United States to evaluate the effectiveness of the CAAA. At the 

core of the monitoring, known as the Temporally Integrated Monitoring of Ecosystems (TIME) project, 

was the concept of a probability survey, where a set of sampling sites was chosen to be statistically 

representative of a target population. In the Northeast (New England and Adirondacks), this target 

population consists of lakes likely to be responsive to changes in rates of acidic deposition. In the 

Mid-Atlantic, the target population is upland streams with a high probability of responding to changes 

in acidic deposition. Repeated surveys of this population allowed an assessment of trends and changes 

in the number of acidic systems during the past decade. The trends reported in the following table 

are for recovery from chronic acidifi cation. The analysis found that during the 1990s, the amount of 

acidic waters in the target population declined. The number of acidic lakes in the Adirondacks dropped 

by 38%, and the number of acidic lakes in New England dropped by 2%. The length of acidic streams 

declined by 28% in the Mid-Atlantic area.

Estimates of change in number and proportion of acidic surface waters in acid-sensitive regions 

of the northern and eastern United States. Estimates are based on applying current rates of 

change in Gran ANCa

 to past estimates of population characteristics from probability surveys.

Region

Number of 

Lakes

Number

Acidicb

%

Acidicc

Time 

Period

of 

Estimate

Current

Rate of

ANC

Changed

Estimated

Number

Currently

Acidice

Current

%

Acidic

%

Change 

in

Number

of Acidic

Systems

New England 6,834 lakes 386 lakes 5.6% 1991–1994 +0.3 374 lakes 5.5% -2%

Adirondacks 1,830 lakes 238 lakes 13.0% 1991–1994 +0.8 149 lakes 8.1% -38%

Mid-Atlantic 42,426 km 5,014 km 11.8% 1993–1994 +0.7 3,600 km 8.5% -28%

a

 For both Northeast lakes and Mid-Atlantic streams, waterbodies with ANC (using the analytical technique of Gran titration, 

with the result known as “Gran ANC”) of < 100 μeq/L are particularly vulnerable.

b

 Number of lakes/streams with Gran ANC < 0 in past probability survey (data collected at “Time Period of Estimate” in column 5).

c

 Percent of population (from Column 2) with Gran ANC < 0 in past probability survey (data collected at “Time Period of Estimate” in column 5). d

 Based on regional trends in μeq/L/year.

e

 Based on trends from repeated surveys through 2001.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 4 Summary and Next Steps

88

Next Steps

In addition to characterizing the biological 

condition of the nation’s stream resources, the 

WSA provides a rich data set that has sparked 

interest in many additional areas of investigation. 

These include the following:

• Support Protection and Restoration 

Actions – The WSA fi nds that between 25 

and 32% of stream length is rated poor due 

to high levels of nutrients or excess streambed 

sedimentation. These streams are two times 

more likely to score poor for biological 

condition than streams with low levels of 

these parameters. This national-scale fi nding 

reinforces reports from states and the USGS 

on specifi c watersheds and stream segments 

that identify nutrients and streambed 

sedimentation as leading water quality 

stressors. EPA is pursuing opportunities to 

use the WSA data in combination with other 

data to inform decision-makers responsible 

for water resource protection and restoration 

actions. Specifi c actions in the short term 

include analyzing the WSA dataset to 

determine associations between watershed 

characteristics (e.g., size, slope, and soil type) 

to help target where improvements are needed; 

using these characteristics in conjunction 

with information on the effectiveness of best 

management practices (BMPs) to help identify 

successful non-point source pollution controls; 

and supporting states’ development of water 

quality standards for nutrients and sediments. 

• Future Designs – It is clear that future 

surveys will continue to be based on sample 

survey designs and that the detection of 

changes and trends will be of greater interest; 

therefore, future survey designs will include 

provision for estimating both current 

status and future trends. This will require a 

determination of the number of sites that are 

revisited versus new sites. Current analyses 

of variance components suggest that in 

future surveys, a substantial percentage of the 

sites (possibly 20–50%) should be replaced 

with new sites and that this replacement 

should continue with each new survey. 

This replacement will help detect change; 

incorporating new sites will improve future 

status assessments and reduce the likelihood 

that bias will be introduced by repeated 

sampling of the same locations. As individual 

states and tribes begin adopting sample survey 

designs into their programs, the results from 

their efforts can be incorporated into the 

national assessments.

• Indicators – This initial assessment was 

unable to incorporate a large set of biological 

and stressor indicators because of a short 

planning timeline. In future national 

stream surveys, the WSA will consider 

including fi sh assemblages, algal assemblages 

(e.g., periphyton in streams), fi sh tissue 

contamination by metals and organics, 

and/or sediment contamination assessed 

through either sediment metal and organic 

chemistry or sediment toxicity tests. It will 

also be possible to add emerging stressor 

indicators of concern. This will allow for 

a more comprehensive assessment of both 

the conditions in wadeable streams and the 

stressors potentially affecting them. 

• Field Protocols – The fi eld protocols used 

for the WSA are widely used and were well 

tested across the country. These protocols 

have demonstrated a strong ability to detect 

environmental signals against the background 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 4 Summary and Next Steps

89

of natural variability. For this initial assessment 

of wadeable streams, using the same protocols 

across the country reduced the complexity of 

interpreting the results; however, for future 

national stream surveys, the use of different 

yet comparable methods will be evaluated for 

different types of streams (e.g., low gradient 

vs. high gradient). EPA and the states will 

also explore integrating and sharing data from 

multiple sources, as well as options to improve 

sample collection methods.

• Reference Conditions – Stream ecologists 

and state and federal managers agree that they 

should be able to describe least-disturbed 

reference condition at a more refi ned spatial 

scale than that of the nine regions presented 

in the WSA. To do so will require substantial 

coordinated efforts among state, tribal, and 

federal partners. There are also likely to be 

some regions of the country in which landuse changes have been so dramatic that even 

the “best” streams may have experienced 

substantial chemical, physical, and biological 

degradation. Additional research will be 

required to provide a better solution to setting 

expected conditions for those regions of the 

country.

• Stressor Ranking – The presentation on 

stressors in the WSA showed both their 

extent (i.e., the percent of stream length with 

excessive levels of the stressors) and relative 

risk (i.e., the increased chance of fi nding poor 

biological condition). To make the best use 

of this information, the WSA must look for 

stressors that have both high relative risk and 

large extent. The human health assessment 

community combines these two sets of 

information into a single number called the 

“population attributable relative risk.” If, 

during investigation, this summary number 

proves reliable for ecological studies, it will 

simplify the ranking of stressors in future 

assessments. However, use of more than one 

biological assemblage in future assessments 

will result in multiple relative risk values, 

one for each biological indicator. It would Photo courtesy of Michael L. Smith, FWS
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Chapter 4 Summary and Next Steps

90

not be surprising if EPA and its partners fi nd 

that the relative risk posed by each stressor 

depends on the biological community being 

evaluated. Although these added numbers may 

complicate the ranking of stressors, they will 

also aid in understanding which component 

of the stream biota is sensitive to each stressor 

and will provide additional options for 

management. 

• Future National Assessments – EPA and its 

state, tribal, and federal partners will produce 

national assessments of waterbody types 

on a yearly cycle. For lakes and reservoirs, 

a fi eld survey will occur in 2007 with a 

national assessment report of the results in 

2009. Rivers will be surveyed in 2008, and 

a national assessment report will follow in 

2010. Wadeable streams will be surveyed 

again in 2009, and the assessment report 

that follows in 2011 will include all fl owing 

waters – both rivers and streams. That report 

will also evaluate any changes in biological 

condition that occurred in streams. An NCCR 

assessment will be repeated in 2012, with the 

results of the fi eld survey from 2010. Wetlands 

will be surveyed during the 2011 sampling 

season, followed by a national assessment 

report in 2013. From that point on, the 

surveys and national assessment reports will be 

repeated in sequence, with changes and trends 

becoming a greater focus for each resource 

survey.

The continued utility of these national surveys 

and their assessment reports requires continued 

consistency in design, as well as in fi eld, lab, 

and assessment methods from assessment to 

assessment; however, the surveys must also 

provide fl exibility that allows the science of 

monitoring to improve over time. Maintaining 

consistency while allowing fl exibility and growth 

will be one of the many challenges facing the 

national assessment program in coming years.

This national survey would not have been 

possible without the involvement of hundreds of 

dedicated scientists working for state, tribal, and 

federal agencies and universities across the United 

States. Future surveys will rely on this continued 

close collaboration, a free exchange of knowledge, 

and a deep well of energy and enthusiasm. It 

is EPA’s goal that participants translate the 

expertise they gained through these national 

surveys to studies of their own waters and use this 

substantial and growing baseline of information 

to evaluate the success of efforts to protect and 

restore the quality of the nation’s waters.

Photo courtesy of National Park Service
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Glossary of Terms 

91

Glossary of Terms

Benthic macroinvertebrates: Aquatic larval 

stages of insects such as dragonflies; aquatic 

insects such as aquatic beetles; crustaceans such 

as crayfish; worms; and mollusks. These small 

creatures live throughout the stream bed attached 

to rocks, vegetation, and logs and sticks or 

burrowed into stream bottoms.

Biological assemblages: Key groups of animals 

and plants—such as benthic macroinvertebrates, 

fish, or algae—that are studied to learn more 

about the condition of water resources.

Biological integrity: State of being capable of 

supporting and maintaining a balanced community of organisms having a species composition, 

diversity, and functional organization comparable 

to that of the natural habitat of the region.

Ecoregions: Ecological regions that are similar in 

climate, vegetation, soil type, and geology; water 

resources within a particular ecoregion have 

similar natural characteristics and similar 

responses to stressors.

In-stream fish habitat: Areas fish need for 

concealment and feeding. These areas include 

large wood within the stream banks, boulders, 

undercut banks, and tree roots. 

Intermittent (ephemeral) streams: Streams that 

flow only during part of the year, such as in the 

spring and early summer after snowmelt.

Macroinvertebrate Index of Biotic Condition: 

The sum of a number of individual measures of 

biological condition, such as the number of taxa 

in a sample, the number of taxa with different 

habits and feeding strategies, etc. 

National Hydrography Dataset: Comprehensive 

set of digital spatial data—based on U.S. Geological Survey 1:100,000 scale topographic maps—

that contains information on surface water 

features such as streams, rivers, lakes, and ponds. 

Nutrients: Substances such as nitrogen and 

phosphorus that are essential to life but can overstimulate the growth of algae and other plants in 

water. Excess nutrients in streams and lakes can 

come from agricultural and urban runoff, leaking 

septic systems, sewage discharges, and similar 

sources.

O/E (Observed/Expected) Ratio of Taxa Loss: 

A ratio comparing the number of taxa expected 

(E) to exist at a site to the number that are 

actually observed (O). The taxa expected at 

individual sites are based on models developed 

from data collected at reference sites.

Perennial streams: Streams that flow 

continuously throughout the year.

Physical habitat: For streams and rivers, the area 

in and around the stream or river, including its 

bed, banks, in­stream and overhanging vegetation, 

and riparian zone.

Probability-based design: A type of random 

sampling technique in which every element of the 

population has a known probability of being 

selected for sampling.

Reach: A discrete segment of a stream.

Reference condition: The least­disturbed 

condition available in an ecological region; 

determined based on specific criteria and used as a 

benchmark for comparison with other sample 

sites in the region.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Glossary of Terms 

92

Riparian: Pertaining to a stream or river and its 

adjacent area.

Riparian disturbance: A measure of the evidence 

of human activities in and alongside streams, such 

as dams, roadways, pastureland, and trash. 

Riparian vegetative cover: Vegetation corridor 

alongside streams and rivers. Intact riparian 

vegetative cover reduces pollution runoff, prevents 

streambank erosion, and provides shade, lower 

temperatures, food, and habitat for fish and other 

aquatic organisms.

Stream order: Stream size, based on the 

confluence of one stream with another. First­order 

streams are the origin or headwaters. The 

confluence or joining of two 1st­order streams 

forms a 2nd­order stream, the confluence of two 

2nd­order streams forms a 3rd­order stream, and 

so on.

Streambed sediments: Fine sediments and silt on 

the streambed. In excess quantities, they can fill in 

the habitat spaces between stream pebbles, 

cobbles, and boulders and suffocate 

macroinvertebrates and fish eggs. 

Stressors: Factors that adversely effect—and 

therefore degrade—aquatic ecosystems. Stressors 

may be chemical (e.g., excess nutrients), physical 

(e.g., excess sediments on the streambed), or 

biological (e.g., competing invasive species). 

Taxa: Plural of taxon; groupings of living 

organisms, such as phylum, class, order, family, 

genus, or species. Scientists organize organisms 

into taxa in order to better identify and 

understand them. 

Transect: A path or line along which one counts 

and studies various aspects of a stream, river, or 

other study area.

Wadeable streams: Streams that are small and 

shallow enough to adequately sample by wading, 

without a boat.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

93

Sources and References

General References

H. John Heinz Center for Science, Economics and the Environment. 2002. The State of the 

Nation’s Ecosystems: Measuring the Lands, Waters, and Living Resources of the United States. 

Cambridge University Press, New York.

National Academy of Public Administration. 2002. Understanding What States Need to Protect 

Water Quality. Academy Project Number 2001-001. Prepared by the National Academy of 

Public Administration, Washington, D.C., for the U.S. Environmental Protection Agency, 

Washington, D.C.

National Geographic Society. 1988. Close-Up: U.S.A. Maps. National Geographic Society, 

Washington, D.C.

NRC (National Research Council). 2001. Assessing the TMDL Approach to Water Quality 

Management. Prepared by the Committee to Assess the Scientifi c Basis of the Total 

Maximum Daily Load Approach to Water Pollution Reduction, Water Science and 

Technology Board, Division of Earth and Life Studies, National Research Council, 

National Academy Press, Washington, D.C.

North American Commission for Environmental Cooperation. 1997. Ecoregions of North 

America (contains level I, II, and III). GIS map fi les. North American Commission for 

Environmental Cooperation, Montreal, Quebec, Canada. 

Stoddard, J.L., J.S. Kahl, F.A. Deviney, D. DeWalle, C.T. Driscoll, A. Herlihy, J.H. Kellogg, 

P. Murdoch, J.R. Webb, and K. Webster. 2003. Response of Surface Water Chemistry to the 

Clean Air Act Amendments of 1990. EPA/620/R-03/001. U.S. Environmental Protection 

Agency, Washington, D.C. 79 pp. 

Strahler, A.N. 1952. Dynamic basis of geomorphology. Geological Society of America Bulletin 

63:923–938.

U.S. Census Bureau. 1990. TIGER line maps: 1990 U.S. Counties. U.S. Department of 

Commerce, U.S. Census Bureau, Washington, D.C.

U.S. Census Bureau. 2001. Your Gateway to Census 2000. U.S. Census Bureau online 

information. U.S. Department of Commerce, U.S. Census Bureau, Washington, D.C. 

Available at http://www.census.gov/main/www/cen2000.html. Accessed May 2006.

U.S. EPA (Environmental Protection Agency). 2001. National Coastal Condition Report. 

EPA 620/R-01/005. U.S. Environmental Protection Agency, Offi ce of Research and 

Development and Offi ce of Water, Washington, D.C.

U.S. EPA (Environmental Protection Agency). 2004. National Coastal Condition Report II. 

EPA 620/R-03/002. U.S. Environmental Protection Agency, Offi ce of Research and 

Development and Offi ce of Water, Washington, D.C.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

94

U.S. EPA (Environmental Protection Agency). 2006. National Estuary Program Coastal 

Condition Report. EPA 842-B-06-001. U.S. Environmental Protection Agency, Offi ce of 

Water and Offi ce of Research and Development, Washington, D.C.

U.S. GAO (General Accounting Offi ce). 2000. Water Quality – Key EPA and State Decisions 

Limited by Inconsistent and Incomplete Data. GAO/RCED-00-54. U.S. Government 

Accountability Offi ce, Washington, D.C.

Vannote, R.L., G.W. Minshall, K.W. Cummins, J.R. Sedell, and C.E. Cushing. 1980. The river 

continuum concept. Canadian Journal of Fisheries and Aquatic Sciences 37:130–137. 

Stream and River Sampling and Laboratory Methods

Barbour, M.T., J. Gerristsen, B.D. Snyder, and J.B. Stribling. 1999. Rapid Bioassessment Protocol

for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates, and Fish, 

Second Edition. EPA 841-B-99-002. U.S. Environmental Protection Agency, Offi ce of 

Water, Washington, D.C.

Peck, D.V., A.T. Herlihy, B.H. Hill, R.M. Hughes, P.R. Kaufmann, D.J. Klemm, J.M. 

Lazorchak, F.H. McCormick, S.A. Peterson, P.L. Ringold, T. Magee, and M.R. Cappaert. 

2006. Environmental Monitoring and Assessment Program – Surface Waters Western Pilot 

Study: Field Operations Manual for Wadeable Streams. EPA 620/R-06/003. U.S. 

Environmental Protection Agency, Offi ce of Research and Development, Washington, 

D.C.

Peck, D.V., D.K. Averill, A.T. Herlihy, R.M. Hughes, P.R. Kaufmann, D.J. Klemm, J.M. 

Lazorchak, F.H. McCormick, S.A. Peterson, M.R. Cappaert, T. Magee, and P.A. Monaco. 

2007. Environmental Monitoring and Assessment Program – Surface Waters Western Pilot 

Study: Field Operations Manual for Non-Wadeable Rivers and Streams. Draft. U.S. 

Environmental Protection Agency, Offi ce of Research and Development, Washington, 

D.C.

U.S. EPA (Environmental Protection Agency). 2004. Wadeable Streams Assessment: Benthic 

Laboratory Methods. EPA 841-B-04-007. U.S. Environmental Protection Agency, 

Offi ce of Water and Offi ce of Environmental Information, Washington, D.C.

U.S. EPA (Environmental Protection Agency). 2004. Wadeable Streams Assessment: Field 

Operations Manual. EPA 841-B-04-004. U.S. Environmental Protection Agency, 

Offi ce of Water and Offi ce of Research and Development, Washington, D.C.

U.S. EPA (Environmental Protection Agency). 2004. Wadeable Streams Assessment: Quality 

Assurance Project Plan. EPA 841-B-04-005. U.S. Environmental Protection Agency, 

Offi ce of Water and Offi ce of Environmental Information, Washington, D.C.

U.S. EPA (Environmental Protection Agency). 2004. Wadeable Streams Assessment: Site 

Evaluation Guidelines. EPA 841-B-04-006. U.S. Environmental Protection Agency, 

Offi ce of Water and Offi ce of Environmental Information, Washington, D.C.

s 
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

95

U.S. EPA (Environmental Protection Agency). 2004. Wadeable Streams Assessment: Water 

Chemistry Laboratory Manual. EPA 841-B-04-008. U.S. Environmental Protection 

Agency, Offi ce of Water and Offi ce of Environmental Information, Washington, D.C.

Probability Designs

Olsen, A.R., J. Sedransk, D. Edwards, C.A. Gotway, W. Liggett, S. Rathbun, K.H. Reckhow, 

and L.J. Young. 1999. Statistical issues for monitoring ecological and natural resources in 

the United States. Environmental Monitoring and Assessment 54:1–45.

Stevens, Jr., D.L. 1997. Variable density grid-based sampling designs for continuous spatial 

populations. Environmetrics 8:167–195.

Stevens, Jr., D.L. and N.S. Urqhart. 2000. Response designs and support regions in sampling 

continuous domains. Environmetrics 11:11–41.

Ecological Regions

Grossman, E. 2002. Watershed: The Undamming of America. Counterpoint, New York, NY.

Hamilton, P.A., T.L. Miller, and D.N. Myers. 2004. Water Quality in the Nation’s Streams and 

Aquifers – Overview of Selected Findings, 1991–2001. U.S. Geological Survey Circular 

1265. U.S. Department of the Interior, U.S. Geological Survey, Reston, VA.

Jacobson, R.B., S.R. Femmer, and R.A. McKenney. 2001. Land-use Change and the Physical 

Habitat of Streams: A Review with Emphasis on Studies within the U.S. Geological Survey 

Federal-State Cooperative Program. U.S. Geological Survey Circular 1175. U.S. 

Department of the Interior, U.S. Geological Survey, Reston, VA.

Laroe, E.T., G.S. Farris, C.E. Puckett, P.D. Doran, and M.J. Mac (ed). 1995. Our Living 

Resources: A Report to the Nation on the Distribution, Abundance, and Health of U.S. Plants, 

Animals, and Ecosystems. U.S. Department of the Interior, National Biological Service, 

Washington, D.C.

Mac, M.J., P.A. Opler, C.E. Puckett Haecker, and P.D. Doran. 1998. Status and Trends of the 

Nation’s Biological Resources – Volumes 1 and 2. U.S. Department of the Interior, U.S. 

Geological Survey, Reston, VA.

Omernik, J.M. 1987. Ecoregions of the conterminous United States. Annals of the Association 

of American Geographers 77:118–125.

Paul, R.K. and R.A. Paul. 1977. Geology of Wisconsin and Upper Michigan. Kendall/Hunt 

Publishing Company, Dubuque, IA.

Secretariat of the Commission for Environmental Cooperation. 1997. Ecological Regions of 

North America – Toward a Common Perspective. Commission for Environmental 

Cooperation, Montreal, Quebec, Canada.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

96

U.S. EPA (Environmental Protection Agency). 2000. National Water Quality Inventory: 

1998 Report to Congress. EPA 841-R-00-001. U.S. Environmental Protection Agency, 

Offi ce of Water, Washington, D.C.

USGS (U.S. Geological Survey). 1999. The Quality of Our Nation’s Waters – Nutrients and 

Pesticides. U.S. Geological Survey Circular 1225. U.S. Department of the Interior, 

U.S. Geological Survey, Reston, VA.

Wohl, E. 2004. Disconnected Rivers – Linking Rivers to Landscapes. Yale University Press, 

New Haven, CT.

Indices of Biotic Integrity

Barbour, M.T., J.B. Stribling, and J.R. Karr. 1995. Multimetric approach for establishing 

biocriteria and measuring biological condition. Chapter 6 In Biological Assessment and 

Criteria: Tools for Water Resource Planning and Decision Making. Edited by W.S. Davis and 

T.P. Simon. Lewis Publishers, Boca Raton, FL.

Frey, D.G. 1977. The integrity of water – An historical approach. In The Integrity of Water. 

Edited by S.K. Ballentine and L.J. Guarala. U.S. Environmental Protection Agency, 

Washington, D.C.

Karr, J.R. and D.R. Dudley. 1981. Ecological perspective on water quality goals. Environmental 

Management 5:55–68.

Karr, J.R. 1981. Assessment of biotic integrity using fi sh communities. Fisheries 6:21–27.

Observed/Expected Models

Hawkins, C.P. 2006. Quantifying biological integrity by taxonomic completeness: Evaluation 

of a potential indicator for use in regional- and global-scale assessments. Ecological 

Applications 16:1251–1266.

Hawkins, C.P., R.H. Norris, J.N. Hogue, and J.W. Feminella. 2000. Development and 

evaluation of predictive models for measuring the biological integrity of streams. 

Ecological Applications 10:1456–1477.

Van Sickle, J., C.P. Hawkins, D.P. Larsen, and A.T. Herlihy. 2005. A null model for the 

expected macroinvertebrate assembalge in streams. Journal of the North American 

Benthological Society 24:178–191.

Wright, J.F. 2000. An introduction to RIVPACS. In Assessing the Biological Quality of Fresh 

Waters. Edited by J.F. Wright, D.W. Sutcliffe, and M.T. Furse. Freshwater Biological 

Association, Ambleside, UK.

Physical Habitat

Kaufmann, P.R., P. Levine, E.G. Robison, C. Seeliger, and D. Peck. 1999. Quantifying Physical 

Habitat in Wadeable Streams. EPA/620/R-99/003. U.S. Environmental Protection Agency, 

Washington, D.C.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

97

Reference Condition

Bailey, R.C., R.H. Norris, and T.B. Reynoldson. 2004. Bioassessment of Freshwater Ecosystems: 

Using the Reference Condition Approach. Kluwer Academic Publishers, New York, NY.

Hughes, R.M. 1995. Defi ning acceptable biological status by comparing with reference 

conditions. In Biological Assessment and Criteria: Tools for Water Resource Planning and 

Decision Making for Rivers and Streams. Edited by W. Davis and T. Simon. Lewis 

Publishing, Boca Raton, FL.

Stoddard, J.L., D.P. Larsen, C.P. Hawkins, R.K. Johnson, and R.H. Norris. 2006. Setting 

expectations for the ecological condition of running waters: The concept of reference 

condition. Ecological Applications 16(4):1267–1276.

Other EMAP Assessments

Stoddard, J.L., D.V. Peck, S.G. Paulsen, J. Van Sickle, C.P. Hawkins, A.T. Herlihy, 

R.M. Hughes, P.R. Kaufmann, D.P. Larsen, G. Lomnicky, A.R. Olsen, S.A. Peterson, 

P.L. Ringold, and T.R. Whittier. 2005. An Ecological Assessment of Western Streams and 

Rivers. EPA 620/R-05/005. U.S. Environmental Protection Agency, Washington, D.C.

Stoddard, J.L., A.T. Herlihy, B.H. Hill, R.M. Hughes, P.R. Kaufmann, D.J. Klemm, J.M. 

Lazorchak, F.H. McCormick, D.V. Peck, S.G. Paulsen, A.R. Olsen, D.P. Larsen, J. Van 

Sickle, and T.R. Whittier. 2006. Mid-Atlantic Integrated Assessment (MAIA) – State of the 

Flowing Waters Report. EPA 620/R-06/001. U.S. Environmental Protection Agency, 

Offi ce of Research and Development, Washington, D.C.

U.S. EPA (Environmental Protection Agency). 2000. Mid-Atlantic Highlands Streams 

Assessment. EPA/903/R-00/015. U.S. Environmental Protection Agency, Region III, 

Philadelphia, PA.

Biological Condition Gradient/Quality of Reference Sites

Davies, S.P. and S.K. Jackson. 2006. The Biological Condition Gradient: A conceptual model 

for interpreting detrimental change in aquatic ecosystems. Ecological Applications 

16:1251–1266.

Lattin, P.D. (In Preparation). A process for characterizing watershed level disturbance using 

orthophotos. Dynamac Corp., Corvallis, OR. (Contact Paul L. Ringold, 

U.S. Environmental Protection Agency, Corvallis, OR.)

Relative Risk

Van Sickle, J., J.L. Stoddard, S.G. Paulsen, and A.R. Olsen. 2006. Using relative risk to 

compare the effects of aquatic stressors at a regional scale. Environmental Management 

38(6):1020–1030.
The Wadeable Streams Assessment: A Collaborative Survey of the Nation’s Streams

Sources and References 

98

Nutrients

Bourassa, N. and A. Cattaneo. 1998. Control of periphyton biomass in Laurentian streams 

(Quebec). Journal of the North American Bentholological Society 17:420–429.

Dodds, W.K. and E.B. Welch. 2000. Establishing nutrient criteria in streams. Journal of the North 

American Benthological Society 19(1):186–196.

Kelly, M.G. 1998. Use of community-based indices to monitor eutrophication in rivers. 

Environmental Conservation 25:22–29.

Kelly, M.G. and B.A. Whitton. 1995. The trophic diatom index: A new index for monitoring 

eutrophication in rivers. Journal of Applied Phycology 7:433–444.

Miltner, R.J. and E.T. Rankin. 1998. Primary nutrients and the biotic integrity of rivers and 

streams. Freshwater Biology 40:145–158.

Nordin, R.N. 1985. Water Quality Criteria for Nutrients and Algae. Ministry of Water, Land and 

Air Protection, Water Management Branch, British Columbia Ministry of the Environment, 

Victoria, British Columbia, Canada. 

Pan, Y., R.J. Stevenson, B.H. Hill, A.T. Herlihy, and G.B. Collins. 1996. Using diatoms as 

indicators of ecological conditions in lotic systems: A regional assessment. Journal of the 

North American Benthological Society 15:481–495.

Welch, E.B. 1992. Ecological Effects of Wastewater. 2nd edition. Chapman and Hall, London, UK.
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